Bug 714579 - Make sure the accessible isn't defunct before getting the caret offset. r=tbsaunde

accessible/src/html/nsHyperTextAccessible.cpp

@@ -1631,6 +1631,9 @@ nsHyperTextAccessible::GetCaretOffset(PRInt32 *aCaretOffset)
   NS_ENSURE_ARG_POINTER(aCaretOffset);
   *aCaretOffset = -1;
 
+  if (IsDefunct())
+    return NS_ERROR_FAILURE;
+
   // Not focused focusable accessible except document accessible doesn't have
   // a caret.
   if (!IsDoc() && !FocusMgr()->IsFocused(this) &&