autoUpdater does not emit an error if quitAndInstall is called without an update to apply

[wearhere]

autoUpdater's docs say that quitAndInstall should only be called after 'update-downloaded' has been emitted, and if it is called before that is emitted, the app will quit but not reopen.

For both these reasons, autoUpdater should emit an error (and not proceed to quit) if quitAndInstall is called without an update to apply.

[wearhere]

Tested by #3838. I would fix this, but I'm not sure if the fix needs to go in Electron or Squirrel.

[zcbenz]

Before someone cares to fix this, I think you can just check whether update-downloaded is fired before calling quitAndInstall.

[wearhere]

Oh for sure. I just think that the auto-updater itself should enforce that restriction since seeing an error is better UX than seeing the app quit and it not come back.

(One simple though perhaps not-totally-correct way to fix this would be to have the auto-updater itself listen for 'update-downloaded' and only allow quitAndInstall to be called thereafter—is that what you were suggesting?)