A recent change caused a regression in the behavior of schannel_recv.

Previously, when no more data was available to read, schannel_recv would return -1. After this change, schannel_recv returns 0:
https://sourceforge.net/p/curl/bugs/1462/

This in turn changes the behavior of curl_easy_recv. It used to return CURLE_AGAIN in this scenario, but now returns CURLE_OK and 0 bytes received, as if we've reached the end of the stream.

This in turn causes HTTPS requests to fail intermittently on Windows with errors like CURLE_GOT_NOTHING.

The behavior is reproducible with libcurl 7.42.1.