MainWindow: Fix use-after-free during shutdown

Remove ConfigChangedCallback in MainWindow's destructor to prevent the
callback from accessing the destroyed MainWindow afterward.

After MainWindow is destroyed UICommon::Shutdown calls
LogManager::Shutdown which ultimately triggers any remaining callbacks.
This resulted in calling MainWindow::OnHardcoreChanged, which crashed in
debug builds and didn't have any obvious effect in release builds.

Source/Core/DolphinQt/MainWindow.cpp

@@ -34,6 +34,7 @@
 #include <qpa/qplatformnativeinterface.h>
 #endif
 
+#include "Common/Config/Config.h"
 #include "Common/ScopeGuard.h"
 #include "Common/Version.h"
 #include "Common/WindowSystemInfo.h"
@@ -277,7 +278,7 @@ MainWindow::MainWindow(Core::System& system, std::unique_ptr<BootParameters> boo
   if (AchievementManager::GetInstance().IsHardcoreModeActive())
     Settings::Instance().SetDebugModeEnabled(false);
   // This needs to trigger on both RA_HARDCORE_ENABLED and RA_ENABLED
-  Config::AddConfigChangedCallback(
+  m_config_changed_callback_id = Config::AddConfigChangedCallback(
       [this]() { QueueOnObject(this, [this] { this->OnHardcoreChanged(); }); });
   // If hardcore is enabled when the emulator starts, make sure it turns off what it needs to
   if (Config::Get(Config::RA_HARDCORE_ENABLED))
@@ -351,6 +352,7 @@ MainWindow::~MainWindow()
   Settings::Instance().ResetNetPlayServer();
 
 #ifdef USE_RETRO_ACHIEVEMENTS
+  Config::RemoveConfigChangedCallback(m_config_changed_callback_id);
   AchievementManager::GetInstance().Shutdown();
 #endif  // USE_RETRO_ACHIEVEMENTS
 

Source/Core/DolphinQt/MainWindow.h

@@ -11,6 +11,10 @@
 #include <optional>
 #include <string>
 
+#ifdef USE_RETRO_ACHIEVEMENTS
+#include "Common/Config/Config.h"
+#endif  // USE_RETRO_ACHIEVEMENTS
+
 #include "Core/Boot/Boot.h"
 
 class QMenu;
@@ -261,6 +265,7 @@ private:
 
 #ifdef USE_RETRO_ACHIEVEMENTS
   AchievementsWindow* m_achievements_window = nullptr;
+  Config::ConfigChangedCallbackID m_config_changed_callback_id;
 #endif  // USE_RETRO_ACHIEVEMENTS
 
   AssemblerWidget* m_assembler_widget;