[3.0] Stop logging an error for every personal message search

[albertlast]

Description

Searching your personal messages puts a row in the error log every time:

2: Undefined array key "start"
url: /index.php?action=pm;sa=search2

Search::performSearch() reads the start twice, and only one of the two guards itself:

$start = (int) ($_GET['start'] ?? 0);
Utils::$context['page_index'] = new PageIndex(..., $start, ...);

// If the supplied start value was invalid, redirect to the correct one.
if ($_GET['start'] != $start) {

A search arrives without a start — only the page links a member clicks afterwards carry one — so the second read fires on the first search anyone runs.

The value is already on hand as $this->start, read once and guarded when the search was set up, so this uses that instead of reading $_GET a third time. PageIndex takes its start by reference and clamps it, which is what makes the comparison below meaningful, so it gets a copy and the original stays to compare against. That is the same shape ItemList::buildPageIndex() uses.

Checked that the redirect still does its job:

request	lands on	log
sa=search2 (POST, no start)	sa=search2	(empty)
sa=search2;start=0	sa=search2;start=0	(empty)
sa=search2;start=999	…;start=0	(empty)
sa=search2;start=-5	…;start=0	(empty)

Same one result found in every case.

Issues References (Fixes|Related|Closes)

n/a