Fixed logging in ngx_http_wait_request_handler().

If c->recv() returns 0 there is no sense in using ngx_socket_errno for
logging, its value meaningless.  (The code in question was copied from
ngx_http_keepalive_handler(), but ngx_socket_errno makes sense there as it's
used as a part of ECONNRESET handling, and the c->recv() call is preceeded
by the ngx_set_socket_errno(0) call.)


git-svn-id: svn://svn.nginx.org/nginx/trunk@5110 73f98a42-aea0-e011-b76d-00259023448c