UI: Fix flash when starting minimized

Rather than showing the main window, then hiding it again when the
tray icon initialization happens, just don't show the main window.

When deciding whether to show the window, we need to know whether
the tray icon is available or not - if it's not and we don't show
the window, there would be no way to restore OBS.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f