Fix bytesAvailable() on UDP under Windows

When ::WSAIoctl() reports 1 byte available for reading, we are trying
to peek an incoming datagram to ensure that the data is actually
delivered. But, according to MSDN docs, we are not allowed to pass NULL
as 'lpNumberOfBytesRecvd' parameter to ::WSARecvFrom() call, if
'lpOverlapped' parameter is also NULL.

The case with an empty datagram is fixed accordingly.

Change-Id: Id13038245332d3fb4bc18038d44a7cfd7ce04775
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/network/socket/qnativesocketengine_win.cpp

@@ -1090,11 +1090,14 @@ qint64 QNativeSocketEnginePrivate::nativeBytesAvailable() const
         WSABUF buf;
         buf.buf = &c;
         buf.len = sizeof(c);
+        DWORD bytesReceived;
         DWORD flags = MSG_PEEK;
-        if (::WSARecvFrom(socketDescriptor, &buf, 1, 0, &flags, 0,0,0,0) == SOCKET_ERROR) {
+        if (::WSARecvFrom(socketDescriptor, &buf, 1, &bytesReceived, &flags, 0,0,0,0) == SOCKET_ERROR) {
             int err = WSAGetLastError();
             if (err != WSAECONNRESET && err != WSAENETRESET)
                 return 0;
+        } else {
+            return bytesReceived;
         }
     }
     return nbytes;

tests/auto/network/socket/qudpsocket/BLACKLIST

@@ -6,7 +6,6 @@ osx
 windows
 osx
 [asyncReadDatagram]
-windows
 osx
 [multicastLeaveAfterClose]
 osx