use negative mob entity ids to avoid conflicts

src/main.c

@@ -118,7 +118,7 @@ void handlePacket (int client_fd, int length, int packet_id, int state) {
           if (mob_data[i].type == 0) continue;
           if ((mob_data[i].data & 31) == 0) continue;
           sc_spawnEntity(
-            client_fd, 65536 + i, recv_buffer,
+            client_fd, -2 - i, recv_buffer,
             mob_data[i].type, mob_data[i].x, mob_data[i].y, mob_data[i].z,
             0, 0
           );