afl-eventtesting: deref of null MarkedSdrObj

Change-Id: I0fe9cb55de114c7e2ad45cd946e94f9c0e93b85c
(cherry picked from commit e63c6fe9)
Reviewed-on: https://gerrit.libreoffice.org/19464Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>

svx/source/svdraw/svdmrkv.cxx

@@ -2007,7 +2007,9 @@ const Rectangle& SdrMarkView::GetMarkedObjRect() const
         Rectangle aRect2;
         for (size_t nm=0; nm<GetMarkedObjectCount(); ++nm) {
             SdrMark* pM=GetSdrMarkByIndex(nm);
-            SdrObject* pO=pM->GetMarkedSdrObj();
+            SdrObject* pO = pM->GetMarkedSdrObj();
+            if (!pO)
+                continue;
             Rectangle aR1(pO->GetSnapRect());
             // apply calc offset to marked object rect
             // ( necessary for handles to be displayed in