[Feature] Alert users when they click the close app button when a encoding task is running

[hustcer]

Thanks for your great work. It really quite helpful.

Is your feature request related to a problem? Please describe.

Alert users when they click the close app button (X on the top right corner) when any encoding task is running, currently the app will exit without any alert, and the user has to restart the encoding task from the beginning. They may have clicked the close button without realizing the serious consequences， or they just want to make the app minimize to the system tray.

Describe the solution you'd like

Alert users when they click the close app button when any encoding task is running, tell the user that there are running encoding tasks and they will lose their work if they exit.

Describe alternatives you've considered

Or simply minimize the app to the system tray. and they can click Exit from the system tray

Additional context

[Alkl58]

Fixed/Added in the new release: v2.1.2