Reimplement the narrowed hot zone for vertical ruler...

... Don't define the TrackPanelCell to be narrower.  Instead, change its
hit-test routine, and only if it is a Wave track.

Previous implementation had the unintended consequence, that a click in the
area excluded from vertical zooming was treated as a click on the background
outside of all tracks, causing de-selection of all tracks.

src/TrackPanel.cpp

@@ -3545,10 +3545,9 @@ void TrackPanelCellIterator::UpdateRect()
          }
          case CellType::VRuler:
             {
-               const int kGuard = 5; // 5 pixels to reduce risk of VZooming accidentally
                mRect.x = kTrackInfoWidth;
                // Right edge of the VRuler is inactive.
-               mRect.width = mPanel->GetLeftOffset() - mRect.x -kGuard;
+               mRect.width = mPanel->GetLeftOffset() - mRect.x;
                mRect.y += kTopMargin;
                mRect.height -= (kBottomMargin + kTopMargin);
             }