Replace GetQueueStatus with PeekMessage(PM_NOREMOVE).

A couple of users report that my recent reworking of the Windows
top-level message loop has led to messages occasionally being lost,
and MsgWaitForMultipleObjects blocking when it ought to have been
called with a zero timeout. I haven't been able to reproduce this
myself, but according to one reporter, PeekMessage(PM_NOREMOVE) is
effective at checking for a non-empty message queue in a way that
GetQueueStatus is not. Switch to using that instead. Thanks to Eric
Flumerfelt for debugging and testing help.

[originally from svn r10057]

windows/window.c

@@ -849,7 +849,8 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
 	int nhandles, n;
         DWORD timeout;
 
-        if (toplevel_callback_pending() || GetQueueStatus(QS_ALLINPUT)) {
+        if (toplevel_callback_pending() ||
+            PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE)) {
             /*
              * If we have anything we'd like to do immediately, set
              * the timeout for MsgWaitForMultipleObjects to zero so