[Qt] Fix a crash when toggling minimalView when --no-embedded-video.

Close #2194
(cherry picked from commit 79579afe)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/main_interface.cpp

@@ -787,7 +787,7 @@ void MainInterface::toggleMinimalView()
     if( i_visualmode != QT_ALWAYS_VIDEO_MODE &&
         i_visualmode != QT_MINIMAL_MODE )
     { /* NORMAL MODE then */
-        if( videoWidget->isHidden() ) emit askBgWidgetToToggle();
+        if( !videoWidget || videoWidget->isHidden() ) emit askBgWidgetToToggle();
         else
         {
             /* If video is visible, then toggle the status of bgWidget */