related tdf#114845 oox: ensure rXShape.is()

Change-Id: Ic5a78d3f650bff82ce8d86a62ecfc025ca2062e0
Reviewed-on: https://gerrit.libreoffice.org/57276
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>
(cherry picked from commit 10272122)
Reviewed-on: https://gerrit.libreoffice.org/57442Reviewed-by: Eike Rathke <erack@redhat.com>

oox/source/export/drawingml.cxx

@@ -2035,7 +2035,7 @@ bool DrawingML::IsInGroupShape () const
 bool DrawingML::IsGroupShape( const Reference< XShape >& rXShape, bool bOrChildShape ) const
 {
     bool bRet = bOrChildShape && IsInGroupShape();
-    if ( !bRet )
+    if ( !bRet && rXShape.is() )
     {
         uno::Reference<lang::XServiceInfo> xServiceInfo(rXShape, uno::UNO_QUERY_THROW);
         bRet = xServiceInfo->supportsService("com.sun.star.drawing.GroupShape");