Fix null pointer dereferences caught by Vigilant Sentry. Ask some questions about some code.

src/LabelDialog.cpp

@@ -330,6 +330,9 @@ bool LabelDialog::TransferDataFromWindow()
             break;
          }
       }
+      wxASSERT(t);
+      if (!t)
+         return false;
 
       // Add the label to it
       if (!rd->title.IsEmpty()) {

src/Menus.cpp

@@ -2967,7 +2967,9 @@ void AudacityProject::OnExportMIDI(){
       return;
    }
 
-   assert(nt);
+   wxASSERT(nt);
+   if (!nt) 
+      return;
 
    while(true){
 

src/TrackArtist.cpp

@@ -969,7 +969,8 @@ void TrackArtist::DrawMinMaxRMS(wxDC &dc, const wxRect &r, const double env[],
       double v;
 
       v = min[x] * env[x];
-      if (mShowClipping && v <= -MAX_AUDIO) {
+      if (clipped && mShowClipping && (v <= -MAX_AUDIO)) 
+      {
          if (clipcnt == 0 || clipped[clipcnt - 1] != xx) {
             clipped[clipcnt++] = xx;
          }
@@ -978,7 +979,8 @@ void TrackArtist::DrawMinMaxRMS(wxDC &dc, const wxRect &r, const double env[],
                        r.height, dB, true, mdBrange, true);
 
       v = max[x] * env[x];
-      if (mShowClipping && v >= MAX_AUDIO) {
+      if (clipped && mShowClipping && (v >= MAX_AUDIO)) 
+      {
          if (clipcnt == 0 || clipped[clipcnt - 1] != xx) {
             clipped[clipcnt++] = xx;
          }
@@ -1128,9 +1130,8 @@ void TrackArtist::DrawIndividualSamples(wxDC &dc, const wxRect &r,
 
       // t0 + clip->GetOffset() is 'h' (the absolute time of the left edge) for 'r'.
       tt = buffer[s] * clip->GetEnvelope()->GetValueAtX(xx + r.x, r, t0 + clip->GetOffset(), pps);
-      if (mShowClipping && (tt <= -MAX_AUDIO || tt >= MAX_AUDIO)) {
+      if (clipped && mShowClipping && ((tt <= -MAX_AUDIO) || (tt >= MAX_AUDIO))) 
          clipped[clipcnt++] = xx;
-      }
       ypos[s] = GetWaveYPos(tt, zoomMin, zoomMax,
                             r.height, dB, true, mdBrange, false);
       if (ypos[s] < -1) {
@@ -2422,12 +2423,13 @@ void TrackArtist::DrawNoteTrack(NoteTrack *track,
    Alg_seq_ptr seq = track->mSeq;
    if (!seq) {
       assert(track->mSerializationBuffer);
-      Alg_track_ptr alg_track = seq->unserialize(track->mSerializationBuffer,
+      // FIX-ME: This is in a clause where we *know* seq is NULL, so why are you dereferencing it?!!! I'm commenting out the rest of this clause.
-            track->mSerializationLength);
+      //Alg_track_ptr alg_track = seq->unserialize(track->mSerializationBuffer,
-      assert(alg_track->get_type() == 's');
+      //      track->mSerializationLength);
-      track->mSeq = seq = (Alg_seq_ptr) alg_track;
+      //assert(alg_track->get_type() == 's');
-      free(track->mSerializationBuffer);
+      //track->mSeq = seq = (Alg_seq_ptr) alg_track;
-      track->mSerializationBuffer = NULL;
+      //free(track->mSerializationBuffer);
+      //track->mSerializationBuffer = NULL;
    }
    assert(seq);
    int visibleChannels = track->mVisibleChannels;

src/TrackPanel.cpp

@@ -1970,7 +1970,8 @@ void TrackPanel::SelectionHandleClick(wxMouseEvent & event,
    }
  
    //Determine if user clicked on a label track. 
-   if (pTrack->GetKind() == Track::Label) {
+   if (pTrack && (pTrack->GetKind() == Track::Label)) 
+   {
       LabelTrack *lt = (LabelTrack *) pTrack;
       if (lt->HandleMouse(event, r,//mCapturedRect,
                           mViewInfo->h, mViewInfo->zoom,
@@ -2164,10 +2165,8 @@ void TrackPanel::ExtendSelection(int mouseXCoordinate, int trackLeftEdge,
    mViewInfo->sel1 = sel1;
    
    //On-Demand: check to see if there is an OD thing associated with this track.  If so we want to update the focal point for the task.
-   if (pTrack->GetKind() == Track::Wave) {
+   if (pTrack && (pTrack->GetKind() == Track::Wave) && ODManager::IsInstanceCreated())
-      if(ODManager::IsInstanceCreated())
+      ODManager::Instance()->DemandTrackUpdate((WaveTrack*)pTrack,sel0); //sel0 is sometimes less than mSelStart
-         ODManager::Instance()->DemandTrackUpdate((WaveTrack*)pTrack,sel0); //sel0 is sometimes less than mSelStart
-   }
 
    // Full refresh since the label area may need to indicate
    // newly selected tracks.
@@ -4524,7 +4523,8 @@ void TrackPanel::HandleResizeDrag(wxMouseEvent & event)
       // minimized heights.
       if (mCapturedTrack->GetLinked()) {
          mInitialUpperTrackHeight = mCapturedTrack->GetHeight();
-         mInitialTrackHeight = link->GetHeight();
+         if (link) // FIX-ME: This wasn't checked previously. Is mInitialTrackHeight safe if this doesn't fire?
+            mInitialTrackHeight = link->GetHeight();
       }
       else if (link) {
          mInitialUpperTrackHeight = link->GetHeight();
@@ -5882,12 +5882,8 @@ void TrackPanel::UpdateVRulerSize()
 /// TrackPanel::OnNextTrack.
 void TrackPanel::OnPrevTrack( bool shift )
 {
-   Track *t;
-   Track *p;
    TrackListIterator iter( mTracks );
-   bool tSelected,pSelected;
+   Track* t = GetFocusedTrack();
-
-   t = GetFocusedTrack();   // Get currently focused track
    if( t == NULL )   // if there isn't one, focus on last
    {
       t = iter.Last();
@@ -5896,18 +5892,21 @@ void TrackPanel::OnPrevTrack( bool shift )
       return;
    }
 
+   Track* p = NULL;
+   bool tSelected = false;
+   bool pSelected = false;
    if( shift )
    {
       p = mTracks->GetPrev( t, true ); // Get previous track
       if( p == NULL )   // On first track
       {
-         wxBell();
+         wxBell(); // ANSWER-ME: Why?
          if( mCircularTrackNavigation )
          {
             TrackListIterator iter( mTracks );
             for( Track *d = iter.First(); d; d = iter.Next( true ) )
             {
-               p = d;
+               p = d; // ANSWER-ME: Is there supposed to be a stopping condition here? If seeking last, why not just use iter.Last()? And what does "d" stand for?!
             }
          }
          else
@@ -5917,7 +5916,8 @@ void TrackPanel::OnPrevTrack( bool shift )
          }
       }
       tSelected = t->GetSelected();
-      pSelected = p->GetSelected();
+      if (p)
+         pSelected = p->GetSelected();
       if( tSelected && pSelected )
       {
          mTracks->Select( t, false );