GeckoCode: Save installation state to savestates

Because of the way this works, randomly overwriting the handler
when loading a savestate will break things because of the
self-modifying nature of the handler.

Source/Core/Core/PatchEngine.cpp

@@ -260,7 +260,7 @@ void Shutdown()
   onFrame.clear();
   speedHacks.clear();
   ActionReplay::ApplyCodes({});
-  Gecko::SetActiveCodes({});
+  Gecko::Shutdown();
 }
 
 }  // namespace