core: bug fix in str2ipbuf, return an error for invalid input parameter

src/core/resolve.c

@@ -1738,7 +1738,7 @@ int str2ipbuf(str* st, ip_addr_t* ipb)
 	/* just in case that e.g. the VIA parser get confused */
 	if(unlikely(!st->s || st->len <= 0)) {
 		LM_ERR("invalid name, no conversion to IP address possible\n");
-		return 0;
+		return -1;
 	}
 	s=(unsigned char*)st->s;