Http2: Always return an error on error

Instead of returning a nullptr in a potential OOM case.

Change-Id: Ib438eaa7550d193cb1207a5d3e48a78b882fa56e
Reviewed-by: Matthias Rauter <matthias.rauter@qt.io>
(cherry picked from commit 238f656d613fc100a8d17ccc980843b39c0056eb)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/access/qhttp2connection.cpp

@@ -859,8 +859,13 @@ QHttp2Connection::createStreamInternal()
     const quint32 streamID = m_nextStreamID;
     if (size_t(m_maxConcurrentStreams) <= size_t(numActiveLocalStreams()))
         return { QHttp2Connection::CreateStreamError::MaxConcurrentStreamsReached };
-    m_nextStreamID += 2;
-    return { createStreamInternal_impl(streamID) };
+
+    if (QHttp2Stream *ptr = createStreamInternal_impl(streamID)) {
+        m_nextStreamID += 2;
+        return {ptr};
+    }
+    // Connection could be broken, we could've ran out of memory, we don't know
+    return { QHttp2Connection::CreateStreamError::UnknownError };
 }
 
 QHttp2Stream *QHttp2Connection::createStreamInternal_impl(quint32 streamID)

src/network/access/qhttp2connection_p.h

@@ -212,6 +212,7 @@ public:
         MaxConcurrentStreamsReached,
         StreamIdsExhausted,
         ReceivedGOAWAY,
+        UnknownError,
     };
     Q_ENUM(CreateStreamError)