fix world previews generation

src/logic/LevelController.cpp

@@ -122,6 +122,7 @@ void LevelController::update(float delta, bool pause) {
 }
 
 void LevelController::processBeforeQuit() {
+    preQuitCallbacks.notify();
     // todo: move somewhere else
     for (auto player : level->players->getAll()) {
         if (player->chunks) {

src/logic/LevelController.hpp

@@ -5,6 +5,7 @@
 #include "BlocksController.hpp"
 #include "ChunksController.hpp"
 #include "util/Clock.hpp"
+#include "util/CallbacksSet.hpp"
 
 class Engine;
 class Level;
@@ -21,6 +22,8 @@ class LevelController {
 
     util::Clock playerTickClock;
 public:
+    CallbacksSet<> preQuitCallbacks;
+
     LevelController(Engine* engine, std::unique_ptr<Level> level, Player* clientPlayer);
 
     /// @param delta time elapsed since the last update