pgsql: ecpg: Fix zero-termination of string generated by intoasc()

ecpg: Fix zero-termination of string generated by intoasc()

intoasc(), a wrapper for PGTYPESinterval_to_asc that converts an
interval to its textual representation, used a plain memcpy() when
copying its result.  This could miss a zero-termination in the result
string, leading to an incorrect result.

The routines in informix.c do not provide the length of their result
buffer, which would allow a replacement of strcpy() to safer strlcpy()
calls, but this requires an ABI breakage and that cannot happen in
back-branches.

Author: Oleg Tselebrovskiy
Reviewed-by: Ashutosh Bapat
Discussion: https://postgr.es/m/bf47888585149f83b276861a1662f7e4@postgrespro.ru
Backpatch-through: 12

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/e77a1c58e338a1aebf00e3ae82d282f8bd32fe17

Modified Files
--------------
src/interfaces/ecpg/compatlib/informix.c           |  2 +-
.../ecpg/test/compat_informix/.gitignore           |  2 ++
src/interfaces/ecpg/test/compat_informix/Makefile  |  3 +-
.../ecpg/test/compat_informix/intoasc.pgc          | 21 ++++++++++++
.../ecpg/test/compat_informix/meson.build          |  1 +
src/interfaces/ecpg/test/ecpg_schedule             |  1 +
.../ecpg/test/expected/compat_informix-intoasc.c   | 40 ++++++++++++++++++++++
.../test/expected/compat_informix-intoasc.stderr   |  0
.../test/expected/compat_informix-intoasc.stdout   |  2 ++
9 files changed, 70 insertions(+), 2 deletions(-)