[BUG] Imap::sort() throws exceptions for empty sets

[psiberx]

Environment:

• PHP IMAP version: 3.1.0
• PHP Version: 7.4.
• Type of execution: Irrelevant

Describe the bug Imap::sort() throws exceptions when there is no error because it incorrectly handles the result of imap_sort() call.

This check:

if (!$result) {
    throw new UnexpectedValueException('Could not sort messages!', 0, self::HandleErrors(\imap_errors(), 'imap_sort'));
}

Should be replaced with:

if ($result === false) {
    throw new UnexpectedValueException('Could not sort messages!', 0, self::HandleErrors(\imap_errors(), 'imap_sort'));
}

https://www.php.net/manual/en/function.imap-sort.php

To Reproduce Call Imap::sort() with criteria that should return an empty set.

Expected behavior No exception.