WIP: Bug 1706445 - Fix for D116146 r=annyG

Differential Revision: https://phabricator.services.mozilla.com/D116519

dom/base/nsFrameLoader.cpp

@@ -3235,7 +3235,9 @@ void nsFrameLoader::RequestFinalTabStateFlush() {
   if (mSessionStoreListener) {
     context->FlushSessionStore();
     mSessionStoreListener->ForceFlushFromParent();
+    if (wgp) {
       wgp->NotifySessionStoreUpdatesComplete(embedder);
+    }
     // No async ipc call is involved in parent only case
     return;
   }
@@ -3250,7 +3252,9 @@ void nsFrameLoader::RequestFinalTabStateFlush() {
 
   FlushPromise::All(GetCurrentSerialEventTarget(), flushPromises)
       ->Then(GetCurrentSerialEventTarget(), __func__, [wgp, embedder]() {
+        if (wgp) {
           wgp->NotifySessionStoreUpdatesComplete(embedder);
+        }
       });
 }