[1.x] fix: allow boolean settings with truthy defaults to be disabled

[huoxin233]

Fixes #4781

Changes proposed in this pull request:

Backport fix #4782 to 1.x

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)

[imorland]

Thanks for the thorough diagnosis in #4781, @huoxin233 — and #4782 is the right fix for 2.x, where buildSettingComponent passes a setting's default through as the fallback, so a truthy default genuinely gets forced back on.

On 1.x, though, that trigger doesn't exist. 1.x's buildSettingComponent calls setting() without a fallback for boolean settings, and no core caller passes a truthy fallback — so fallback is always '', and '' || '' and '' ?? '' behave identically. There's no code path in 1.x core where this change alters behaviour.

The only way to encounter it on 1.x is an extension passing a truthy fallback to setting() for a boolean, which is easily handled extension-side (omit the truthy fallback, or read the default explicitly).

With 1.x now in security/critical-fix-only wind-down ahead of its end of life, we're keeping changes to it minimal, so I'm going to close this one for 1.x. The fix lives on where it's actually needed, in #4782 for 2.x. Really appreciate the report and the clear write-up. 🙏