[3.0] Stop the buddy and ignore lists erroring when they are empty

[albertlast]

Description

Profile → Buddies and Ignore List is an error page for any member who has not added a buddy — which is every member on a new forum:

Database error, given array of integer values is empty. (buddy_list)
Function: retrieveUserData

BuddyIgnoreLists::buddies() runs its query unconditionally:

$buddies = User::loadCustom(
	[
		'where' => ['mem.id_member IN ({array_int:buddy_list})'],
		'limit' => \count(Profile::$member->buddies),
		'params' => ['buddy_list' => Profile::$member->buddies],
	],
	UserDataset::Profile,
);

An empty array in {array_int:} is a hard database error in SMF's query layer, not a query that matches nothing. ignore() has the same shape and the same problem.

2.1 had the guard — Sources/Profile-Modify.php:

if (!empty($buddiesArray))
{
	$result = $smcFunc['db_query']('', '
		SELECT id_member
		FROM {db_prefix}members
		WHERE id_member IN ({array_int:buddy_list})
	…

It was lost when this moved to User::loadCustom(). Both lists now skip the query when there is nothing to look up, which leaves $buddies / $ignored as the empty arrays the rest of each method already copes with — count() for buddy_count, then a foreach that does not run.

Checked

On the running forum, as an admin with no buddies and nobody ignored. Before: both pages render the error, and smf_log_errors gains a row per visit. After: both render their "Add to buddy list" / "Add to ignore list" forms, and nothing is logged.

Found while sweeping every page of a stock forum for fatals, alongside #9405.

Issues References (Fixes|Related|Closes)

Related to #7933