rtpengine: rework media-address fix by checking if value is specified

Thanks go to @wangduanduan for reporting it in #2692

modules/rtpengine/rtpengine.c

@@ -1827,6 +1827,7 @@ static int parse_flags(struct ng_flags_parse *ng_flags, struct sip_msg *msg,
 					err = "missing value";
 					if (!val.s)
 						goto error;
+					break;
 				} else if (str_eq(&key, "received-from")) {
 					if (val.s)
 						ng_flags->received_from = val;