pgsql: Fix some null pointer dereferences in LDAP auth code

Fix some null pointer dereferences in LDAP auth code

An LDAP URL without a host name such as "ldap://" or without a base DN
such as "ldap://localhost" would cause a crash when reading pg_hba.conf.

If no binddn is configured, an error message might end up trying to print a
null pointer, which could crash on some platforms.

Author: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>
Reviewed-by: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>

Branch
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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0bcdab58e83b2ac2caf4bd78e1583c11df97d4f1

Modified Files
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src/backend/libpq/auth.c | 3 ++-
src/backend/libpq/hba.c | 6 ++++--
2 files changed, 6 insertions(+), 3 deletions(-)