Fix crash under Milk style

diff --git a/style/qtcurve.cpp b/style/qtcurve.cpp
index 5f95f66..9f06adb 100644
--- a/style/qtcurve.cpp
+++ b/style/qtcurve.cpp
@@ -8106,7 +8106,7 @@
             }
         }
 
-        if(opts.shadeMenubarOnlyWhenActive && SHADE_WINDOW_BORDER==opts.shadeMenubars &&
+        if(itsMdiColors && opts.shadeMenubarOnlyWhenActive && SHADE_WINDOW_BORDER==opts.shadeMenubars &&
            itsActiveMdiColors[ORIGINAL_SHADE]==itsMdiColors[ORIGINAL_SHADE])
             opts.shadeMenubarOnlyWhenActive=false;