security check on parent widget (just in case)

src/gui/UBDockPalette.cpp

@@ -511,7 +511,10 @@ void UBDockPalette::moveTabs()
     if(eUBDockTabOrientation_Down == mTabsOrientation)
     {
         if (mOrientation == eUBDockOrientation_Right)
+        {
+            if (parentWidget())
                 y = parentWidget()->height() - border()- mTabWidgets.size() * TABSIZE;
+        }
         else
             y = height() - border()- mTabWidgets.size() * TABSIZE;
     }