The old regex requires something after the 'host' part. Fix this.

Old regex is : /^GRANT\s(.+)\sON\s(.+)\sTO\s(.*)@(.*?)(\s.*)$/ . The
last part (\s.*)$ means "a space followed by anything". The issue is
that when user has no GRANT privileges, the "SHOW GRANTS FOR #{user_string}" returns
"GRANT SELECT ON `database`.* TO 'user'@'%'" which does not match (\s.*)$ .
This small patch fixes this making last bloc optional (thanks to '?').