Bug 424097 - Crash when running runtests.py --a11y, and having JAWS running at the same time, patch=marcoz, r=me, ab5=beltzner

accessible/src/base/nsAccessible.cpp

@@ -2199,6 +2199,8 @@ nsAccessible::GetAttributesInternal(nsIPersistentProperties *aAttributes)
     if (!sameTypeParent || sameTypeParent == docShellTreeItem)
       break;
     nsIDocument *parentDoc = doc->GetParentDocument();
+    if (!parentDoc)
+      break;
     startContent = parentDoc->FindContentForSubDocument(doc);      
   }