Resolves: tdf#112017 crash on particular odt

Change-Id: I6ba2e73562a16afecb6abdfe4f1a40b1e316379e
Reviewed-on: https://gerrit.libreoffice.org/41685
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

svx/source/unodraw/unoshape.cxx

@@ -3034,7 +3034,8 @@ void SvxShape::setAllPropertiesToDefault()
         mpObj->SetMergedItem(Svx3DCharacterModeItem(true));
     }
 
-    mpModel->SetChanged();
+    if (mpModel)
+        mpModel->SetChanged();
 }
 
 void SvxShape::setPropertiesToDefault(