Bug 637621, allow selection collapse more often, r+a=jst

--HG--
extra : rebase_source : 216a2405f929ca00cc4982ebb39230b4f3018dc1

layout/generic/nsSelection.cpp

@@ -4933,6 +4933,9 @@ nsTypedSelection::Collapse(nsINode* aParentNode, PRInt32 aOffset)
     return NS_ERROR_INVALID_ARG;
   if (!mFrameSelection)
     return NS_ERROR_NOT_INITIALIZED; // Can't do selection
+
+  nsCOMPtr<nsINode> kungfuDeathGrip = aParentNode;
+
   mFrameSelection->InvalidateDesiredX();
   if (!IsValidSelectionPoint(mFrameSelection, aParentNode))
     return NS_ERROR_FAILURE;