MDL-52831 users: Do not delete Mr. and Mrs. Whitespace accounts
MDL-52831 users: Do not delete Mr. and Mrs. Whitespace accounts

Due to imperfect validation of the user registration and profile forms,
we allowed for firstname and lastname be just a whitespace. On MySQL,
such a whitespace is not significant for VARCHAR comparison so these
otherwise valid accounts could be silently deleted.

The patch makes sure that at least one of the checked fields is a real
empty string before deleting such account.

dilawar/moodle