pgsql: Avoid platform-dependent infinite loop in pg_dump.

Avoid platform-dependent infinite loop in pg_dump.

If malloc(0) returns NULL, the binary search in findSecLabels() will
probably go into an infinite loop when there are no security labels,
because NULL-1 is greater than NULL after wraparound.

(We've seen this pathology before ... I wonder whether there's a way to
detect the class of bugs automatically?)

Diagnosis and patch by Steve Singer, cosmetic adjustments by me

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/febda37fda469317f15b0acadfbdedab3d7dc793

Modified Files
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src/bin/pg_dump/pg_dump.c |   11 +++++++++--
1 files changed, 9 insertions(+), 2 deletions(-)