commit fix for crash if you undo whilst time-shifting a track, found and produced by Campbell Barton

src/Menus.cpp

@@ -3521,6 +3521,11 @@ void AudacityProject::OnUndo()
       return;
    }
 
+   // can't undo while dragging
+   if (mTrackPanel->IsMouseCaptured()) {
+      return;
+   }
+
    TrackList *l = mUndoManager.Undo(&mViewInfo.sel0, &mViewInfo.sel1);
    PopState(l);
 

src/TrackPanel.cpp

@@ -3185,6 +3185,13 @@ bool TrackPanel::IsDragZooming()
    return (abs(mZoomEnd - mZoomStart) > DragThreshold);
 }
 
+/// Determines if drag zooming is active
+bool TrackPanel::IsMouseCaptured()
+{
+   return (mMouseCapture != IsUncaptured);
+}
+
+
 ///  This actually sets the Zoom value when you're done doing
 ///  a drag zoom.
 void TrackPanel::DragZoom(wxMouseEvent & event, int trackLeftEdge)

src/TrackPanel.h

@@ -252,6 +252,7 @@ class AUDACITY_DLL_API TrackPanel:public wxPanel {
    virtual void OnTrackSolo(bool shiftdown, Track *t = NULL);
    virtual void OnTrackClose();
    virtual Track * GetFirstSelectedTrack();
+   virtual bool IsMouseCaptured();
 
    virtual void EnsureVisible(Track * t);