s3: Fix early tldap_search cancels

s3: Fix early tldap_search cancels

A callback of tldap_search_send might not interested in the rest of the results
and could do a TALLOC_FREE of the search request. In this case, "subreq" is
already free'ed. So we have to set it to pending before the callback is called.
The TALLOC_FREE of the search request will set it to non-pending again via
tldap_msg_destructor.

Autobuild-User: Volker Lendecke <vlendec@samba.org>
Autobuild-Date: Sun Mar 20 11:26:57 CET 2011 on sn-devel-104