Bug 1011736 - Added null check to Accessible::Shutdown.

accessible/src/generic/Accessible.cpp

@@ -2461,7 +2461,7 @@ Accessible::Shutdown()
 
   mContent = nullptr;
   mDoc = nullptr;
-  if (SelectionMgr()->AccessibleWithCaret(nullptr) == this)
+  if (SelectionMgr() && SelectionMgr()->AccessibleWithCaret(nullptr) == this)
     SelectionMgr()->ResetCaretOffset();
 }