prevent peekmessage from crashing when msg == NULL

[Eric Frias]

This is another patch for all platforms.  Somewhere, for some reason, our
client code was calling PeekMessage(NULL, ...), basically asking windows to
discard a single message without returning it.  From the MSDN docs, this
seems like an illegal use of the function, but Windows does the right thing
when we do it and wine crashes.

Eric
-------------- next part --------------
A non-text attachment was scrubbed...
Name: peekmessage.diff
Type: application/octet-stream
Size: 998 bytes
Desc: not available
Url : http://www.winehq.org/pipermail/wine-patches/attachments/20041117/3078bef0/peekmessage.obj