fix read notification in QWindowsPipeReader::waitForPipeClosed

In QWindowsPipeReader::waitForPipeClosed we must check for available
bytes in the internal buffer and trigger the notified signal.

This fixes tst_QLocalSocket::writeToClientAndDisconnect on Windows.

Change-Id: I0f4d6cd73a0a8eac5b438b82984457068a9551d1
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

src/corelib/io/qwindowspipereader.cpp

@@ -318,6 +318,7 @@ bool QWindowsPipeReader::waitForPipeClosed(int msecs)
     QElapsedTimer stopWatch;
     stopWatch.start();
     forever {
+        waitForReadyRead(0);
         checkPipeState();
         if (pipeBroken)
             return true;