[LyX/master] Fix problem with drawing of math backround with selections.

[Richard Heck]

commit 3e681bea4fa3f0d24016187d9778ab8344b93592
Author: Enrico Forestieri <for...@lyx.org>
Date:   Wed May 7 14:18:14 2014 -0400

    Fix problem with drawing of math backround with selections.

diff --git a/src/mathed/InsetMathHull.cpp b/src/mathed/InsetMathHull.cpp
index f7215e9..eb11bc2 100644
--- a/src/mathed/InsetMathHull.cpp
+++ b/src/mathed/InsetMathHull.cpp
@@ -510,7 +510,7 @@ void InsetMathHull::drawBackground(PainterInfo & pi, int x, 
int y) const
                return;
        } 
        pi.pain.fillRectangle(x + 1, y - dim.asc + 1, dim.wid - 2,
-                       dim.asc + dim.des - 1, backgroundColor(pi));
+                       dim.asc + dim.des - 1, pi.backgroundColor(this));
 }