Correct state when exiting Android application (resolves #787, close #765)

templates/android/template/app/src/main/java/org/libsdl/app/SDLActivity.java

@@ -384,6 +384,9 @@ public class SDLActivity extends Activity {
     public static void handleNativeExit() {
         SDLActivity.mSDLThread = null;
         mSingleton.finish();
+
+        // This fixes bad state errors when calling exit from C++, then resuming later
+        System.exit(0);
     }