Revert "auth: fix error check"

This reverts commit b7772a0.

Author: l2dy

modules/auth/auth_mod.c

@@ -442,7 +442,7 @@ static inline int pv_authorize(struct sip_msg* msg, str *domain,
 	cred = (auth_body_t*)h->parsed;
 
 	res = auth_get_ha1(msg, &cred->digest.username, domain, ha1);
-	if (res != 0) {
+	if (res < 0) {
 		/* Error */
 		if (sigb.reply(msg, 500, &auth_500_err, NULL) == -1) {
 			LM_ERR("failed to send 500 reply\n");