[PATCH] remove assert(ch->auth_user_request != NULL)

external ACL soemtimes cannot find the credentials in ACL Checklist even
if they are attached to the HTTPRequest object.

This seems to happen when the checklist is created and the line match
started before the credentials are known.

Unless someone knows of a better place to duplicate the credentials
reference from request to checklist. I would like to apply this patch to:

  * locate the %LOGIN value from either place where credentials can be
found,
  * updates the checklist if it was unset,
  * passes '-' to the helper if no credentials at all were given.

Although the earlier logics forcing a lookup means this '-' case should
not happen.

Amos

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