Incorrect users search by last visit time in memberlist.php

Currently members search with last visit time involved yields incorrect results (or no results where it shouldn't be the case), also the related memberlist.php code (https://github.com/phpbb/phpbb/blob/3.2.x/phpBB/memberlist.php#L1076) is inconsistent with the similar  code of ACP prune users module (which works correctly https://github.com/phpbb/phpbb/blob/3.2.x/phpBB/includes/acp/acp_prune.php#L474-L486).