Patch for event-msw.c crash (cygwin version)

Hi, I can easily get assert (!badly_p); to fail in cygwin version on my machine (e.g. by running gnus and partly opening/closing the XEmacs window by some other window). From the code and my understanding of the select function it seems to me that that assert should never happen if the select works according to specs. Hence it looks like a bug in the cygwin's select implementation. The attached patch avoids the bug. It is ugly, but saves from crashes and should do no harm even if the bug gets fixed. The patch is against 21.2.b25 source. Thanks. -- Cheers, -Dima.