Author: altsysrq
Description:
'ug_group' column in 'user_groups' table limited to 16 characters, but when modifying rights directly from LocalSettings.php configuration file, group with longer name can be added, like:
$wgGroupPermissions['copy_upload_access']['upload_by_url'] = true;
will show 'copy_upload_access' in groups list in administration panel, but no user can be added to this group, because 'copy_upload_access' is 17 characters length.
Some check of validity of at least $wgGroupPermissions should be added.