Bug 1145724 - adding null check before creating treewalker in nsAccessibilityService::ContentRemoved r=surkov

---
 accessible/base/nsAccessibilityService.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

accessible/base/nsAccessibilityService.cpp

@@ -533,8 +533,9 @@ nsAccessibilityService::ContentRemoved(nsIPresShell* aPresShell,
     // accessibles in subtree then we don't care about the change.
     Accessible* child = document->GetAccessible(aChildNode);
     if (!child) {
-      a11y::TreeWalker walker(document->GetContainerAccessible(aChildNode),
-                              aChildNode, a11y::TreeWalker::eWalkCache);
+      Accessible* container = document->GetContainerAccessible(aChildNode);
+      a11y::TreeWalker walker(container ? container : document, aChildNode,
+                              a11y::TreeWalker::eWalkCache);
       child = walker.NextChild();
     }