Check for Updates button throws an error on unsupported platforms

[DinCahill]

OS
Linux (non-AppImage)
Development builds (any OS)

Gmail Desktop Version
v3.0.0-alpha.34

Describe the bug
When using the deb package, the "Check for Updates" button throws an error because app-update.yml does not exist.

When developing via npm run start, it's dev-app-update.yml instead.

Steps to reproduce the behavior

1. Click the top-left menu > Gmail Desktop > Check for Updates...
2. Error message appears

Expected behavior
The option should not be shown, or should not throw an error.

Media

Additional context
This presumably affects anything not supported by electron-updater: deb, rpm, Arch etc.

I tried simply checking if path.join(app.getAppPath(), '..', 'app-update.yml') exists, and that worked as expected on Windows, Mac, Linux AppImage, and Linux deb.

---

For testing electron-updater in development, the documentation says this:

Note that in order to develop/test UI/UX of updating without packaging the application you need to have a file named dev-app-update.yml in the root of your project, which matches your publish setting from electron-builder config (but in yaml format). But it is not recommended, better to test auto-update for installed application (especially on Windows). Minio is recommended as a local server for testing updates.

Example dev-app-update.yml for GitHub:

provider: github
owner: timche
repo: gmail-desktop
channel: dev