Fix crash in SingleApplication when other end exits immediately

In those cases the emit might cause the server to remove the connection
and we are working with a dangling pointer. We can't call putChar on
that, so acknowledge the message immediately and then emit the message.

third_party/SingleApplication-3.3.0/singleapplication_p.cpp

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