Fix a compilation warning, make some member functions const

src/NoteTrack.cpp

@@ -218,7 +218,7 @@ void NoteTrack::WarpAndTransposeNotes(double t0, double t1,
    Alg_iterator iter(mSeq, false);
    iter.begin();
    Alg_event_ptr event;
-   while ((event = iter.next()) && event->time < t1) {
+   while (0 != (event = iter.next()) && event->time < t1) {
       if (event->is_note() && event->time >= t0 &&
           // Allegro data structure does not restrict channels to 16.
           // Since there is not way to select more than 16 channels,

src/Track.cpp

@@ -270,7 +270,7 @@ void Track::ReorderList(bool resize)
 }
 #endif
 
-bool Track::IsSyncLockSelected()
+bool Track::IsSyncLockSelected() const
 {
 #ifdef EXPERIMENTAL_SYNC_LOCK
    AudacityProject *p = GetActiveProject();
@@ -278,7 +278,7 @@ bool Track::IsSyncLockSelected()
       return false;
 
    SyncLockedTracksIterator git(mList);
-   Track *t = git.First(this);
+   Track *t = git.First(const_cast<Track*>(this));
 
    if (!t) {
       // Not in a sync-locked group.

src/Track.h

@@ -206,7 +206,7 @@ class AUDACITY_DLL_API Track: public XMLTagHandler
    virtual double GetEndTime() const = 0;
 
    // Checks if sync-lock is on and any track in its sync-lock group is selected.
-   bool IsSyncLockSelected();
+   bool IsSyncLockSelected() const;
 };
 
 struct TrackListNode

src/WaveTrack.cpp

@@ -1631,7 +1631,7 @@ AUDACITY_DLL_API sampleCount WaveTrack::TimeToLongSamples(double t0) const
    return (sampleCount)floor(t0 * mRate + 0.5);
 }
 
-double WaveTrack::LongSamplesToTime(sampleCount pos)
+double WaveTrack::LongSamplesToTime(sampleCount pos) const
 {
    return ((double)pos) / mRate;
 }

src/WaveTrack.h

@@ -303,7 +303,7 @@ class AUDACITY_DLL_API WaveTrack: public Track {
     * @param pos The time number of samples from the start of the track to convert.
     * @return The time in seconds.
     */
-   double LongSamplesToTime(sampleCount pos);
+   double LongSamplesToTime(sampleCount pos) const;
 
    // Get access to the clips in the tracks. This is used by
    // track artists and also by TrackPanel when sliding...it would