[ticket/11548] Run array_map on complete error array and not just colour_error

Up to now the array_map() that turns error messages into the localized output
was only ran if the group's color was set. With this patch it'll run the
array_map() on the complete error array if it's not empty.

Ticket: http://tracker.phpbb.com/browse/PHPBB3-11548

PHPBB3-11548