QLocalSocket/Win: fix possible UB in _q_pipeClosed()

We must stop the pipe writer before closing the handle on which it
operates.

Pick-to: 5.15 6.0 6.1
Change-Id: I4765dd8393167fe2453653aba76a097b8ace8e3d
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

src/network/socket/qlocalsocket_win.cpp

@@ -260,13 +260,10 @@ void QLocalSocketPrivate::_q_pipeClosed()
     emit q->disconnected();
 
     pipeReader->stop();
+    delete pipeWriter;
+    pipeWriter = nullptr;
     destroyPipeHandles();
     handle = INVALID_HANDLE_VALUE;
-
-    if (pipeWriter) {
-        delete pipeWriter;
-        pipeWriter = 0;
-    }
 }
 
 qint64 QLocalSocket::bytesAvailable() const