Properly fix #825

We should read the message before sending the ack!

third_party/SingleApplication-3.3.0/singleapplication_p.cpp

@@ -494,12 +494,14 @@ void SingleApplicationPrivate::slotDataAvailable( QLocalSocket *dataSocket, quin
     if ( !isFrameComplete( dataSocket ) )
         return;
 
+    auto message = dataSocket->readAll();
+
     writeAck( dataSocket );
 
     ConnectionInfo &info = connectionMap[dataSocket];
     info.stage = StageConnectedHeader;
 
-    Q_EMIT q->receivedMessage(instanceId, dataSocket->readAll());
+    Q_EMIT q->receivedMessage(instanceId, message);
 }
 
 void SingleApplicationPrivate::slotClientConnectionClosed( QLocalSocket *closedSocket, quint32 instanceId )