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
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/771240f972ee7a3da8bbc3fa247e698144ecea15

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 ++++++++++++
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 ++
8 files changed, 69 insertions(+), 2 deletions(-)