[Android] Minor postInvalidateWindowSurface JNI cleanup

android/android_studio_project/app/src/main/java/jp/xenia/emulator/WindowedAppActivity.java

@@ -85,6 +85,7 @@ public abstract class WindowedAppActivity extends Activity {
     }
 
     // Used from the native WindowedAppContext. May be called from non-UI threads.
+    @SuppressWarnings("UnusedDeclaration")
     protected void postInvalidateWindowSurface() {
         if (mWindowSurfaceView == null) {
             return;

src/xenia/ui/windowed_app_context_android.cc

@@ -336,6 +336,7 @@ void AndroidWindowedAppContext::Shutdown() {
     ui_thread_looper_ = nullptr;
   }
 
+  activity_method_post_invalidate_window_surface_ = nullptr;
   activity_method_finish_ = nullptr;
   if (activity_) {
     ui_thread_jni_env_->DeleteGlobalRef(activity_);