Bug 1840626 - Fix debug Crash [@ mozilla::dom::ReadableStream::CloseNative] r=saschanaz

The assertion dereferences Algorithms(), which could have been freed, so only assert if it exists.

Differential Revision: https://phabricator.services.mozilla.com/D187149

dom/streams/ReadableStream.cpp

@@ -1345,8 +1345,8 @@ already_AddRefed<ReadableStream> ReadableStream::CreateByteNative(
 
 // https://streams.spec.whatwg.org/#readablestream-close
 void ReadableStream::CloseNative(JSContext* aCx, ErrorResult& aRv) {
-  MOZ_ASSERT(mController->GetAlgorithms()->IsNative());
-
+  MOZ_ASSERT_IF(mController->GetAlgorithms(),
+                mController->GetAlgorithms()->IsNative());
   // Step 1: If stream.[[controller]] implements ReadableByteStreamController,
   if (mController->IsByte()) {
     RefPtr<ReadableByteStreamController> controller = mController->AsByte();

dom/webtransport/test/xpcshell/test_close.js

@@ -65,3 +65,13 @@ add_task(async function test_webtransport_create() {
 
   wt.close();
 });
+
+// bug 1840626 - cancel and then close
+add_task(async function test_wt_stream_create_bidi_cancel_close() {
+  let wt = new WebTransport("https://" + host + "/success");
+  await wt.ready;
+
+  await wt.createBidirectionalStream();
+  await wt.incomingBidirectionalStreams.cancel(undefined);
+  wt.close();
+});