Bug 2622 - Track name overlay is opaque

Somewhere along the line the 'rect' passed in to DrawTrackName()changed
from being for the track area to being for the name area.  Accordingly
the track rect now has to be explicitly accessed from the track to get
its height, from which the transparency is then derived.

src/TrackPanel.cpp

@@ -1069,7 +1069,7 @@ void DrawTrackName(
    // Tracks more than kTranslucentHeight will have maximum translucency for shields.
    const int kOpaqueHeight = 44;
    const int kTranslucentHeight = 124;
-   int h = rect.GetHeight();
+   int h = TrackView::Get( *t ).GetHeight();
    // f codes the opacity as a number between 0.0 and 1.0
    float f = wxClip((h-kOpaqueHeight)/(float)(kTranslucentHeight-kOpaqueHeight),0.0,1.0);
    // kOpaque is the shield's alpha for tracks that are not tall