pgsql: Fix comparisons of pointers with zero to compare with NULL inste

Fix comparisons of pointers with zero to compare with NULL instead.

Per C standard, these are semantically the same thing; but saying NULL
when you mean NULL is good for readability.

Marti Raudsepp, per results of INRIA's Coccinelle.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=bfd3f37be309c3647844aed937e6a66aad5fd3cb

Modified Files
--------------
src/backend/regex/regc_lex.c    |    2 +-
src/backend/utils/adt/tsrank.c  |    2 +-
src/backend/utils/fmgr/dfmgr.c  |    2 +-
src/bin/pg_dump/pg_backup_tar.c |    2 +-
src/port/dirmod.c               |    2 +-
src/timezone/zic.c              |   12 ++++++------
6 files changed, 11 insertions(+), 11 deletions(-)