Qt: fix crash in customize toolbar dialog.

For some reasons, this doesn't crash on Linux...
(cherry picked from commit 25d37a4930519c5bcabbe2c0fae8c86e38d9ea54)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/dialogs/toolbar.cpp

@@ -647,17 +647,15 @@ inline int DroppingController::getParentPosInLayout( QPoint point )
     QPoint origin = mapToGlobal ( point );
 
     QWidget *tempWidg = QApplication::widgetAt( origin );
+    if( tempWidg == NULL )
+        return -1;
 
-    int i = -1;
-    if( tempWidg != NULL)
-    {
-        i = controlLayout->indexOf( tempWidg );
+    int i = controlLayout->indexOf( tempWidg );
     if( i == -1 )
     {
         i = controlLayout->indexOf( tempWidg->parentWidget() );
         tempWidg = tempWidg->parentWidget();
     }
-    }
 
     /* Return the nearest position */
     if( ( point.x() - tempWidg->x()  > tempWidg->width() / 2 ) && i != -1 )