HTTP/2 - do not set END_HEADERS if we have CONTINUATIONs

Setting END_HEADERS flag on a HEADERS frame means we do not have
CONTINUATION frame(s). So do NOT set it too early, only if we
fit into a single frame.

Change-Id: I891a2db227cee59e4eacfe7c2f18b431cd85fe47
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/network/access/http2/http2frames.cpp

@@ -478,6 +478,7 @@ bool FrameWriter::writeHEADERS(QAbstractSocket &socket, quint32 sizeLimit)
         sizeLimit = quint32(maxPayloadSize);
 
     if (quint32(frameBuffer.size() - frameHeaderSize) <= sizeLimit) {
+        addFlag(FrameFlag::END_HEADERS);
         updatePayloadSize();
         return write(socket);
     }

src/network/access/qhttp2protocolhandler.cpp

@@ -328,7 +328,7 @@ bool QHttp2ProtocolHandler::sendHEADERS(Stream &stream)
 {
     using namespace HPack;
 
-    outboundFrame.start(FrameType::HEADERS, FrameFlag::PRIORITY | FrameFlag::END_HEADERS,
+    outboundFrame.start(FrameType::HEADERS, FrameFlag::PRIORITY,
                         stream.streamID);
 
     if (!stream.data()) {