As the keyboard is released asynchronously after setting the ibus
engine, there's a possibility that the `this._reloading` property
changed in the meantime.

To ensure that `holdKeyboard()` and `releaseKeyboard()` are correctly
paired, record the condition in a local variable so that it maintains
its value in the callback.

Part-of: <!3476>
(cherry picked from commit fb58ceb4)