Bug 1818630 - Crash in [@ mozilla::dom::ReadableStreamReaderGenericRelease]. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D172057

dom/streams/ReadableStream.cpp

@@ -952,6 +952,14 @@ already_AddRefed<Promise> ReadableStream::IteratorReturn(
       return nullptr;
     }
 
+    MOZ_DIAGNOSTIC_ASSERT(
+        reader->GetStream(),
+        "We shouldn't have a null stream here (bug 1821169).");
+    if (!reader->GetStream()) {
+      aRv.Throw(NS_ERROR_FAILURE);
+      return nullptr;
+    }
+
     // Step 4.2. Perform ! ReadableStreamDefaultReaderRelease(reader).
     ReadableStreamDefaultReaderRelease(aCx, reader, aRv);
     if (NS_WARN_IF(aRv.Failed())) {

dom/streams/ReadableStreamDefaultReader.cpp

@@ -285,7 +285,7 @@ void ReadableStreamReaderGenericRelease(ReadableStreamGenericReader* aReader,
 
   // Step 4. If stream.[[state]] is "readable", reject reader.[[closedPromise]]
   // with a TypeError exception.
-  if (aReader->GetStream()->State() == ReadableStream::ReaderState::Readable) {
+  if (stream->State() == ReadableStream::ReaderState::Readable) {
     aReader->ClosedPromise()->MaybeRejectWithTypeError(
         "Releasing lock on readable stream");
   } else {