rtpproxy: allow 0 as value for ice candidate avp

- reported by GH #1003

src/modules/rtpproxy/rtpproxy.c

@@ -2326,7 +2326,7 @@ force_rtp_proxy(struct sip_msg* msg, char* str1, char* str2, int offer,
 					&ice_candidate_priority_val, 0)
 				== NULL) {
 			ice_candidate_priority_val.n = 2;
-		} else if ((ice_candidate_priority_val.n < 1) ||
+		} else if ((ice_candidate_priority_val.n < 0) ||
 				(ice_candidate_priority_val.n > 2)) {
 			LM_ERR("invalid ice candidate priority value %d\n",
 					ice_candidate_priority_val.n);