Bug 788639 - crash in GetPrintCanvasElementsInFrame @ mozilla::layout::FrameChildListIterator::FrameChildListIterator, r=smaug

layout/generic/nsSimplePageSequence.cpp

@@ -496,6 +496,9 @@ nsSimplePageSequenceFrame::StartPrint(nsPresContext*   aPresContext,
 void
 GetPrintCanvasElementsInFrame(nsIFrame* aFrame, nsTArray<nsRefPtr<nsHTMLCanvasElement> >* aArr)
 {
+  if (!aFrame) {
+    return;
+  }
   for (nsIFrame::ChildListIterator childLists(aFrame);
     !childLists.IsDone(); childLists.Next()) {