Bug 1750211 - Return an error in unexpected state. r=necko-reviewers,kershaw

Differential Revision: https://phabricator.services.mozilla.com/D136005

netwerk/protocol/http/Http3Stream.cpp

@@ -273,6 +273,7 @@ nsresult Http3Stream::OnReadSegment(const char* buf, uint32_t count,
       break;
     default:
       MOZ_ASSERT(false, "We are done sending this request!");
+      rv = NS_ERROR_UNEXPECTED;
       break;
   }