[PATCH] wininet: do avoid overwriting the buffer (Coverity)

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=25714

Your paranoid android.


=== WXPX64 (32 bit http) ===
http.c:4291: Test failed: 4462: expected status 100 got 10
http.c:4291: Test failed: 4506: expected status 100 got 40
http.c:4264: Test failed: ar->dwResult = 0, expected 1
http.c:4291: Test failed: 4515: expected status 70 got 100
http: unhandled exception c0000005 at 7722EDEA

=== WXPX64 (64 bit http) ===
http.c:4291: Test failed: 4462: expected status 100 got 10
http.c:4291: Test failed: 4506: expected status 100 got 40
http.c:4264: Test failed: ar->dwResult = 0, expected 1
http.c:4291: Test failed: 4515: expected status 70 got 100
http: unhandled exception c0000005 at 0000000000495D94