Bug 1429215: Null-check pointer before using it in assertion in GetFloatFromPlaceholder() (to avoid crashing during assertion). r=mats

MozReview-Commit-ID: 7pWq8nr1mqQ

--HG--
extra : rebase_source : c4cb90d7f865a3ab52889b53695f94f3e4157298

layout/base/nsLayoutUtils.cpp

@@ -1708,7 +1708,7 @@ nsLayoutUtils::GetFloatFromPlaceholder(nsIFrame* aFrame) {
   if (aFrame->GetStateBits() & PLACEHOLDER_FOR_FLOAT) {
     nsIFrame *outOfFlowFrame =
       nsPlaceholderFrame::GetRealFrameForPlaceholder(aFrame);
-    NS_ASSERTION(outOfFlowFrame->IsFloating(),
+    NS_ASSERTION(outOfFlowFrame && outOfFlowFrame->IsFloating(),
                  "How did that happen?");
     return outOfFlowFrame;
   }