Bug 1359995: Add back the null-check on curData. r=heycam

I removed it, but seems it can be hit. It'd be nice to have a test-case where it
fails though...

MozReview-Commit-ID: 7Xa3dNHwFMn

--HG--
extra : rebase_source : 7f0d8df2f571b84745c41bf675f12a9340016775

layout/base/RestyleTracker.h

@@ -350,7 +350,9 @@ RestyleTracker::AddPendingRestyle(Element* aElement,
       // to reach aElement in the case the PresShell posts a restyle event from
       // PostRecreateFramesFor, so we need to track it here.
       MOZ_ASSERT(curData, "expected to find a RestyleData for cur");
-      curData->mDescendants.AppendElement(aElement);
+      if (curData) {
+        curData->mDescendants.AppendElement(aElement);
+      }
     }
   }