fix(tags): defer policy if min primary & secondary tags 0

[DavideIadeluca]

2.x equivalent to #4277

Fixes #4276

Changes proposed in this pull request:
Early return if minimum number of primary and secondary tags is 0. Deferring it rather then force allowing in that case allows other policies to take action

Reviewers should focus on:

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)