pgsql: ltree: Zero padding bytes when allocating memory for externally

ltree: Zero padding bytes when allocating memory for externally visible data.

ltree/ltree_gist/ltxtquery's headers stores data at MAXALIGN alignment,
requiring some padding bytes. So far we left these uninitialized. Zero
those by using palloc0.

Author: Andres Freund
Reported-By: Andres Freund / valgrind / buildarm animal skink
Backpatch: 9.1-

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/814570418d5e6bccb766efbe86d27aef206e5511

Modified Files
--------------
contrib/ltree/_ltree_gist.c  | 14 +++++++-------
contrib/ltree/_ltree_op.c    |  8 ++++----
contrib/ltree/ltree_gist.c   | 10 +++++-----
contrib/ltree/ltree_op.c     |  6 +++---
contrib/ltree/ltxtquery_io.c |  2 +-
5 files changed, 20 insertions(+), 20 deletions(-)