The LDAP rebinding was still using the old blowfish encryption instead
of AES so rebinding failed.

This reverts commit 88833bac.
and fixes FS#2874

Renderers that set the format to xhtml don't necessarily inherit from
Doku_Renderer_xhtml, this reverts a prior change that introduced the
stricter parameter type.

replace boolean conditional checks on possibly uninitialized vars with \!empty/empty/isset as appropriate