android: now run exit() from Java side, as the next engine run is expected to be clean

android/app/src/main/java/su/xash/engine/XashActivity.java

@@ -30,6 +30,18 @@ public class XashActivity extends SDLActivity {
         AndroidBug5497Workaround.assistActivity(this);
     }
 
+    @Override
+    public void onDestroy()
+    {
+        super.onDestroy();
+
+        // Now that we don't exit from native code, we need to exit here, resetting
+        // application state (actually global variables that we don't cleanup on exit)
+        //
+        // When the issue with global variables will be resolved, remove that exit() call
+        System.exit(0);
+    }
+
     @Override
     protected String[] getLibraries() {
         return new String[]{"SDL2", "xash"};