wininet: Don't peek data in InternetQueryDataAvailable if there is no more to be expected.

[Misha Koshelev]

I am going to send a more complete try2 patchset tomorrow (the patch as
given is correct but there are some more problems with
InternetQueryDataAvailable that need to be fixed, like the fact that it
actually doesn't return ERROR_NO_MORE_FILES when all HTTP data has been
retrieved).

Misha