pgsql: Properly handle empty arrays returned from plperl functions.

Properly handle empty arrays returned from plperl functions.

Bug reported by David Wheeler, fix by Alex Hunsaker.
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch master
# Changes to be committed:
# (use "git reset HEAD <file>..." to unstage)
#
# modified: src/pl/plperl/plperl.c
#
# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# autom4te.cache/
# configure.in~
# doc/src/sgml/ref/grant.sgml~
# src/backend/port/win32_latch.c~
# src/bin/psql/command.c~
# src/include/pg_config.h.win32~
# src/pl/plpython/plpython.c~
# src/tools/msvc/pgbison.bat~
# src/tools/msvc/pgbison.pl.bak
# src/tools/msvc/pgflex.bat~
# src/tools/msvc/pgflex.pl.bak
# src/tools/pgindent/README~
# src/tools/pgindent/pgindent.pl
# src/tools/pgindent/pgindent.pl~
# xxxxx
# yyyyyy

Branch
------
REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/22a55b3af687806e6b3a08a131d00541774eaade

Modified Files
--------------
src/pl/plperl/plperl.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)