Bug 1228652 - Check for window.closed after flushing messages in navigateAndRestore. r=mossop

MozReview-Commit-ID: 9Cgxg9A61O7

--HG--
extra : rebase_source : 719b990b7490175839c48bf2a74f40891b0ad2ed

browser/components/sessionstore/SessionStore.jsm

@@ -2509,7 +2509,7 @@ var SessionStoreInternal = {
       let window = tab.ownerDocument && tab.ownerDocument.defaultView;
 
       // The tab or its window might be gone.
-      if (!window || !window.__SSi) {
+      if (!window || !window.__SSi || window.closed) {
         return;
       }