Avoid invalidating best size for foreground/background color change

(cherry picked from commit beffb32d2d)

src/gtk/window.cpp

@@ -4408,9 +4408,6 @@ void wxWindowGTK::GTKApplyWidgetStyle(bool forceStyle)
         g_object_unref(style);
 #endif
     }
-
-    // Style change may affect GTK+'s size calculation:
-    InvalidateBestSize();
 }
 
 void wxWindowGTK::DoApplyWidgetStyle(GtkRcStyle *style)
@@ -4718,6 +4715,7 @@ bool wxWindowGTK::SetFont( const wxFont &font )
         // apply style change (forceStyle=true so that new style is applied
         // even if the font changed from valid to wxNullFont):
         GTKApplyWidgetStyle(true);
+        InvalidateBestSize();
     }
 
 #ifdef __WXGTK3__