In a few cases, reverse a condition and eliminate a return.

This should improve the diagnostic and progress reports.

Patch by Chris Angelico.

Patch by Xiang Zhang.

* Replace "fd = -1" with "fd = INVALID_SOCKET"
* Replace "fd < 0" with "fd == INVALID_SOCKET": SOCKET_T is unsigned on Windows

Bug found by Pavel Belikov ("Fragment N1"):
http://www.viva64.com/en/b/0414/#ID0ECDAE

Bug found by Pavel Belikov ("Fragment N1"):
http://www.viva64.com/en/b/0414/#ID0ECDAE

Patch by Alakshendra Yadav.

Patch by Xiang Zhang.