Review wikula_adminapi_ClearReferrers()

[hvorragend]

This function seems to have some errors for me.

The $tag should never be empty.
the $where clause should never be empty.
In pntemplates/wikula_user_referrers.tpl:77

<form action="<!--[pnmodurl modname='wikula' type='admin' func='ClearReferrers' tag=$tag]-->" method="post" enctype="application/x-www-form-urlencoded" id="form_clearrefform">

It seems that a user can delete referrers for a tag, so we need to make more check in this case...the user is allow to delete this tag.