Bug 1414 - (Residual) Green triangles in scrub bar sometimes appear and sometimes don't

The residual bug was that the PlayHead triangle could appear when in the scrub ruler.  This was an 'off by 2' error in using the size of that region.

src/widgets/Ruler.cpp

@@ -2278,6 +2278,9 @@ void AdornedRulerPanel::UpdateRects()
 #else
       auto qpHeight = mScrubZone.height - scrubHeight;
       bottom = &mScrubZone, topHeight = qpHeight;
+      // Increase scrub zone height so that hit testing finds it and
+      // not QP region, when on bottom 'edge'.
+      mScrubZone.height+=BottomMargin;
 #endif
 
       top->height = topHeight;