UI: Set default source toolbar visibility to true

This significantly simplifies the
configuration setting's initial load.

This also fixes as issue where the source toolbar
would initialise as "TextLabel" with enabled
buttons if the user had not yet toggled the setting.

Fixes #3722
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