[ofw] Opensm & WinMad: a race, cauing BSOD722

[Hefty, Sean]

> Two ideas:
> WmProviderInit() is called without checking the return status. Is there a
> reason ?
> Seems like the similar patch is needed for WvIoDeviceControl().

I can't tell whether IOCTLs suffer from the same problem or not.  But since Windows is stupid, I went ahead and added the same protection to winverbs, plus some additional validation in case we get a cleanup event for a file for which we failed to create.

- Sean