Fix infinite loop in ns_turn_server.c (#1460)

In case ur_map_get returns 1 server will enter infinite loop because
newid != 0.

Co-authored-by: Asmir <asmir.mehic@viber.com>

src/server/ns_turn_server.c

@@ -700,6 +700,7 @@ static mobile_id_t get_new_mobile_id(turn_turnserver *server) {
     uint64_t sid = server->id;
     sid = sid << 56;
     do {
+      newid = 0;
       while (!newid) {
         if (TURN_RANDOM_SIZE == sizeof(mobile_id_t)) {
           newid = (mobile_id_t)turn_random();