Fix uid parsing for ldap keyserver
Fix uid parsing for ldap keyserver

* src/engine-gpg.c (gpg_keylist_preprocess): Check field count
for uid and add fallback.

--
This fixes accessing unintialized memory and resulting
crashes in gpgrt_asprintf.

GnuPG-Bug-Id: T3550

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme