Default MIDI track height is enough to display velocity slider...

... It is computed from the layout table, and in fact comes to 158 pixels,
versus 150 for other tracks.

src/TrackPanel.h

@@ -118,6 +118,8 @@ private:
 #endif
 
 public:
+   static unsigned DefaultNoteTrackHeight();
+
    LWSlider * GainSlider(WaveTrack *t, bool captured = false) const;
    LWSlider * PanSlider(WaveTrack *t, bool captured = false) const;
 
@@ -920,6 +922,7 @@ enum : int {
    kTrackInfoSliderHeight = 25,
    kTrackInfoSliderWidth = 84,
    kTrackInfoSliderAllowance = 5,
+   kTrackInfoSliderExtra = 5,
 };
 
 #ifdef USE_MIDI