CharacterMap: avoid white outline around selected character

SetLowColor() to the highlighting colour before drawing a selected character
to avoid blending with the regular white background.

src/apps/charactermap/CharacterView.cpp

@@ -439,6 +439,7 @@ CharacterView::Draw(BRect updateRect)
 						y + fCharacterHeight - fGap));
 
 					SetHighColor(color);
+					SetLowColor(highlight);
 				}
 
 				// Draw character