pgsql: Fix incorrect results for numeric data passed through an ECPGSQ

Fix incorrect results for numeric data passed through an ECPG SQLDA.

Numeric values with leading zeroes were incorrectly copied into a
SQLDA (SQL Descriptor Area), leading to wrong results in ECPG programs.

Report and patch by Daisuke Higuchi.  Back-patch to all supported
versions.

Discussion: https://postgr.es/m/1803D792815FC24D871C00D17AE95905C71161@g01jpexmbkw24

Branch
------
REL_11_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/68393f3fd6b91f1f61a2bdb4e59eb439256eeb65

Modified Files
--------------
src/interfaces/ecpg/ecpglib/sqlda.c                |  34 +-
src/interfaces/ecpg/test/expected/sql-sqlda.c      | 108 ++---
src/interfaces/ecpg/test/expected/sql-sqlda.stderr | 436 +++++++++++++--------
src/interfaces/ecpg/test/expected/sql-sqlda.stdout |  28 ++
src/interfaces/ecpg/test/sql/sqlda.pgc             |   4 +-
5 files changed, 380 insertions(+), 230 deletions(-)