Ensure FT stay "running in background" on MacOS after all window closed

[PikachuEXE]

Pull Request Type

• Bugfix
• Feature Implementation
• Documentation
• Other

Related issue

Fixes #2934

Description

I think FT already stay "running in background" on MacOS after closing all windows, but only once (due to calling once instead of on in main app code)
This PR simply changes once to on for window-all-closed event

Screenshots

Done in dev mode, so you can see the dock icon is Electron, and part of dev tool as FT window

Screen.Recording.2023-05-11.at.09.14.30.mov

Testing

• Get on a MacOS (even VM)
• Open app
• Close window
• Ensure FT dock icon lit (still running)
• Click on dock icon
• Ensure window created
• Close window (2nd time)
• Ensure FT dock icon lit (still running) (2nd time)

Desktop

• OS: MacOS
• OS Version:
• FreeTube version:

Additional context

[efb4f5ff-1298-471a-8973-3d47447115dc]

@QAQDE Check out the screen recording in the PR body is this the behavior u want to see?

[QAQDE]

@QAQDE Check out the screen recording in the PR body is this the behavior u want to see?

Yes, it now looks completely fine. Thanks