tdf#93188 - avoid crash in media player.

ToggleFloatingMode can be run during dispose, and should handle that,
thanks to Maxim Monastirsky for the analysis.

Change-Id: I72c5aff9b75fa2c1b6795e239370244dafdafae2
Reviewed-on: https://gerrit.libreoffice.org/17931Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

avmedia/source/framework/mediaplayer.cxx

@@ -101,12 +101,16 @@ void MediaFloater::ToggleFloatingMode()
 {
     ::avmedia::MediaItem aRestoreItem;
 
+    if (mpMediaWindow)
         mpMediaWindow->updateMediaItem( aRestoreItem );
     delete mpMediaWindow;
     mpMediaWindow = NULL;
 
     SfxDockingWindow::ToggleFloatingMode();
 
+    if (isDisposed())
+        return;
+
     mpMediaWindow = new MediaWindow( this, true );
 
     mpMediaWindow->setPosSize( Rectangle( Point(), GetOutputSizePixel() ) );