UI: Fix preview disabled in studio mode

If OBS is set to minimize to system tray on startup and studio mode is
enabled, the preview would be disabled when showing OBS, if the preview
in non studio mode was disabled.
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