fix(Core/Crash): Fix a crash occurring when shutting the server down.

src/server/game/Maps/MapUpdater.cpp

@@ -67,6 +67,7 @@ MapUpdater::~MapUpdater()
 
 void MapUpdater::activate(size_t num_threads)
 {
+    _workerThreads.reserve(num_threads);
     for (size_t i = 0; i < num_threads; ++i)
     {
         _workerThreads.push_back(std::thread(&MapUpdater::WorkerThread, this));
@@ -83,7 +84,10 @@ void MapUpdater::deactivate()
 
     for (auto& thread : _workerThreads)
     {
-        thread.join();
+        if (thread.joinable())
+        {
+            thread.join();
+        }
     }
 }