don't bother with lobby id free list

src/ServerState.cc

@@ -189,10 +189,11 @@ vector<shared_ptr<Lobby>> ServerState::all_lobbies() {
 }
 
 shared_ptr<Lobby> ServerState::create_lobby() {
-  shared_ptr<Lobby> l(new Lobby(this->next_lobby_id++));
-  if (!this->id_to_lobby.emplace(l->lobby_id, l).second) {
-    throw logic_error("lobby already exists with the given id");
+  while (this->id_to_lobby.count(this->next_lobby_id)) {
+    this->next_lobby_id++;
   }
+  shared_ptr<Lobby> l(new Lobby(this->next_lobby_id++));
+  this->id_to_lobby.emplace(l->lobby_id, l);
   l->log.info("Created lobby");
   return l;
 }

src/ServerState.hh

@@ -99,9 +99,6 @@ struct ServerState {
   std::vector<std::shared_ptr<Lobby>> public_lobby_search_order_v1;
   std::vector<std::shared_ptr<Lobby>> public_lobby_search_order_non_v1;
   std::vector<std::shared_ptr<Lobby>> public_lobby_search_order_ep3;
-  // TODO: Use a free-list instead of an incrementer to prevent wrap-around
-  // behavioral bugs. This... will probably never be an issue for anyone, but we
-  // technically should handle it.
   std::atomic<int32_t> next_lobby_id;
   uint8_t pre_lobby_event;
   int32_t ep3_menu_song;