pgsql: Avoid multiple free_struct_lconv() calls on same data.

Avoid multiple free_struct_lconv() calls on same data.

A failure partway through PGLC_localeconv() led to a situation where
the next call would call free_struct_lconv() a second time, leading
to free() on already-freed strings, typically leading to a core dump.
Add a flag to remember whether we need to do that.

Per report from Thom Brown. His example case only provokes the failure
as far back as 9.4, but nonetheless this code is obviously broken, so
back-patch to all supported branches.

Branch
------
REL9_3_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/0c4457de8b8a6aa715bdfe94ecfa8ee3d48e2827

Modified Files
--------------
src/backend/utils/adt/pg_locale.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)