PreviewVideoActivity: ensure player is stopped when closing fullscreen

This already worked for onBackPressed

Signed-off-by: Álvaro Brey Vilas <alvaro.brey@nextcloud.com>

src/main/java/com/owncloud/android/ui/preview/PreviewVideoActivity.java

@@ -90,7 +90,7 @@ public class PreviewVideoActivity extends FileActivity implements OnCompletionLi
         exoPlayer = new SimpleExoPlayer.Builder(this).build();
         playerView.setPlayer(exoPlayer);
 
-        findViewById(R.id.exo_exit_fs).setOnClickListener(v -> finish());
+        findViewById(R.id.exo_exit_fs).setOnClickListener(v -> onBackPressed());
 
         if (mSavedPlaybackPosition >= 0) {
             exoPlayer.seekTo(mSavedPlaybackPosition);