Bug 1692862 - Null out mSession pointer when closing Http2Stream r=dragana,necko-reviewers

The Http2Stream holds a raw pointer to the Http2Session which gets initialized in the constructor and is never changed.
We should null out the member so we don't attempt to use it after it has been destroyed.

Differential Revision: https://phabricator.services.mozilla.com/D105188

netwerk/protocol/http/Http2Stream.cpp

@@ -1162,6 +1162,7 @@ void Http2Stream::Close(nsresult reason) {
   ClearPushSource();
 
   mTransaction->Close(reason);
+  mSession = nullptr;
 }
 
 void Http2Stream::SetResponseIsComplete() {