This back-patches commit 0c5783ff30 into the
9.3 branch. At the time, Heikki just thought he was fixing an unlikely
integer-overflow scenario, but in point of fact the original coding was
hopelessly broken: it supposed that escape_json never enlarges the data
more than 2X, which is wrong on its face. The revised code eliminates
making any a-priori assumptions about the output length.
Per report from Saul Costa. The bogus code doesn't exist before 9.3,
so no other branches need fixing.
f44290b7b3