Request body: explicit handling of NGX_AGAIN. Request body reading indirectly uses the "do { c->recv() } while (c->read->ready)" form, which is not really correct, as for example with SSL c->read->ready may be still set when c->recv() returns NGX_AGAIN due to SSL_ERROR_WANT_WRITE (see 7351:2b5528023f6b), and therefore this form might be an infinite loop. Added explicit NGX_AGAIN handling for the sake of correctness.