Catch and log potentially missing 'dm4_topicmap_id' cookie-value.

Currently any request (from a HTTP-Client) which is missing (resp.
does not know 'Topicmaps') the 'dm4_topicmap_id' cookie-value and
involves the 'ka2.geo_object' fails hard (500).

This commit catches and logs the error in the getFacetTypes()-
implementation which is hooked into preSend- and postUpdate-Hooks.