pgsql: Avoid reading past datum end when parsing JSON.

Avoid reading past datum end when parsing JSON.

Several loops in the JSON parser examined a byte in memory just before
checking whether its address was in-bounds, so they could read one byte
beyond the datum's allocation.  A SIGSEGV is possible.  New in 9.3, so
no back-patch.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/66008564f8ce570f7ad6368fbde2138e946d328b

Modified Files
--------------
src/backend/utils/adt/json.c |   21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)