fix: stop fixAmps() recursing forever on a navbar link with an entity

[nabbi]

Automated PR, tested in a zm-holodeck sandbox. An AI agent (Claude Opus 5.5) reproduced the bug on a disposable ZoneMinder built from upstream master 6c0f976c2, wrote this fix and ran the checks below on the same lab. Minimal human review before opening: please review it as you would any contributor's PR.

TL;DR

• Fixes: Left navbar answers 500 when ZM_WEB_NAVBAR_LINKS contains an HTML entity #5209: the left navbar answers 500 when ZM_WEB_NAVBAR_LINKS contains an HTML entity.
• Change: fixAmps() becomes one preg_replace() that escapes every & that doesn't start a character reference; a second commit stops the per-page warnings for navbar links without a query string. 1 file, +9/-15.
• Heads-up, a small behaviour change: which ampersands get escaped changes slightly (table below). Links with entities render again; the escaping is now consistent.
• Tested: 5 link shapes: 3 answered 500 before, all 5 answer 200 after with the link in the page and no PHP warnings.

Details: change, behaviour changes, checks

Before

Upstream master 6c0f976c2: [entity], [two-entities], [bare-and-entity] HTTP 500 (Allowed memory size of 536870912 bytes exhausted ... functions.php on line 1828); [plain], [bare-amp] 200.

Change

• web/skins/classic/includes/functions.php fixAmps(): preg_replace('/&(?!#[0-9]+;|#x[0-9a-f]+;|[a-z][a-z0-9]*;)/i', '&', $html) replaces the recursive search. (Passing the missing offset would also stop the recursion, but keeps the old check, which accepted a bare & whenever any ; came later and escaped hex references.)
• Same file, second commit: read the view of a navbar link only when its href has a query string.

Behaviour changes

Change	Who sees it	Intended / collateral	Alternatives looked into	Chosen, why	Tested by
Links with an entity render instead of a 500	left-navbar users	intended	—	—	probe
A bare & is now escaped even when a ; appears later in the string (was left as is)	admins writing navbar links	collateral	add the missing offset, keep the old check	one rule for every &: escape unless it starts a decimal, hex or named reference	probe [bare-and-entity]
Hex references (&) are kept (were escaped to &)	same	collateral	—	they are valid references	probe
No more Undefined array key and parse_str() lines per page	log readers	intended	—	—	probe

After

Branch at 34a032188 (base 6c0f976c2): 5/5 HTTP 200, link in page, no PHP lines.

Check	Result
holodeck checks	script tests PASS=28; smoke PASS=11 XFAIL=1 (known); ui suite green apart from known XFAILs

Not run: release-1.38 (same code; the patches apply with git am -3).

refs #5209

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