dirmngr: Workaround for a certain broken LDAP URL

* dirmngr/ldap.c (url_fetch_ldap): Detect and replace.

The actual URL causing this is

ldap://ldap.dgnservice.de:389/CN=CRL-1,O=DGN%20Service%20GmbH,\
C=DE?certificateRevocationList?base?objectClass=cRLDistributionPoint

It is actually not very helpful because I had problems finding the
issuer cert:

CN=dgnservice CRL2101 13:PN,O=DGN Deutsches Gesundheitsnetz \
Service GmbH,C=DE