pgsql: Fix error detection in contrib/pgcrypto's encrypt_iv() and decry

Fix error detection in contrib/pgcrypto's encrypt_iv() and decrypt_iv().

Due to oversights, the encrypt_iv() and decrypt_iv() functions failed to
report certain types of invalid-input errors, and would instead return
random garbage values.

Marko Kreen, per report from Stefan Kaltenbrunner

Branch
------
REL8_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/b4e9fd4df3045ccca73a71b656b0fcbbc3c202f5

Modified Files
--------------
contrib/pgcrypto/pgcrypto.c |    8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)