Bug 1479277 - Don't try to send APZ messages after teardown. r=botond

MozReview-Commit-ID: 8l0h197hfTj

--HG--
extra : rebase_source : a65b07f66a05b9ec54aa859fa0d9384061332120

dom/ipc/TabChild.cpp

@@ -532,7 +532,7 @@ TabChild::DoUpdateZoomConstraints(const uint32_t& aPresShellId,
                                   const ViewID& aViewId,
                                   const Maybe<ZoomConstraints>& aConstraints)
 {
-  if (!mApzcTreeManager) {
+  if (!mApzcTreeManager || mDestroyed) {
     return false;
   }