[1.x & 2.x] [Flags] Improved handling of unset community guidelines

[claudiushenrichs]

Current Behavior

If no "Community Guidelines URL" is set in the flarum-flags settings the frontend will show "undefined" on 2.x

On 1.x an empty link is shown: <a>Community-Richtlinien</a>

Steps to Reproduce

1. In /admin#/extension/flarum-flags make sure no community guidelines URL is set
2. On the forum frontend report any message
3. Observe the text next to the "Inappropriate" option

Expected Behavior

If no guidelines URL is set the "Inappropriate" reporting option should probably simply just omit that reference and state "This post is offensive or abusive"

Screenshots

No response

Environment

Flarum versions 1.8.15 and 2.0.0-beta8

Output of php flarum info

No response

Possible Solution

No response

Additional Context

No response