Fix incorrect redirection

[DL6ER]

What does this implement/fix?

We should not try to apply settings levels (incl. all the consequences such as ill-fated redirects) when we have already detected that there are no expert-settings elements on this page.

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Related issue or feature (if applicable): https://github.com/pi-hole/web/issues/2992

Pull request in docs with documentation (if applicable): N/A

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• [x] The code change is tested and works locally.
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[rdwebdesign]

Now Gravity Update page works, but All Settings page is empty (even using the toggle button).

[DL6ER]

Now we recall why the code was there :-) Should be fixed.

[rdwebdesign]

Now:

• Gravity Update page works (no matter what settings level is selected),
• All Settings page is also works,
• BUT... if you select Expert level, the expert pages on the menu are only visible if you are in a Settings page. If you are in a different page (Example: /index), the menu will show only the Basic pages.

We need to run applyExpertSettings() in all pages, but we need a different redirect rule.

We should redirect only:

• if we are inside any Settings pages (something like if ( $(".settings-selector").length !== 0 )) AND
• if we ended up with an empty page (no visible boxes) after switching to Basic level.

[rdwebdesign]

The original issue is $(".box:visible").length will be zero in 2 cases:

• the page contains only "invisible" boxes (this is how we are identifying empty boxes);
• the page has no .box elements at all (this causes the issue in Gravity page and can also cause issues in other pages without this element).

Suggestion:

Revert all commits and change this code:

    // If we left with an empty page (no visible boxes) after switching from
    // Expert to Basic settings, redirect to admin/settings/system instead
-   if ($(".box:visible").length === 0) {
+   if ($(".settings-selector").length !== 0 && $(".box:visible").length === 0) {
      window.location.href = "/admin/settings/system";
    }

This will trigger the redirect only if:

• class settings-selector is present (this class is present in every settings pages, but not in other pages) AND
• there are no visible boxes (the page is empty)