pgsql: libpq_pipeline: Must strdup(optarg) to avoid crash

libpq_pipeline: Must strdup(optarg) to avoid crash

I forgot to strdup() when processing argv[]. Apparently many platforms
hide this mistake from users, but in those that don't you may get a
program crash. Repair.

Per buildfarm member drongo, which is the only one in all the buildfarm
manifesting a problem here.

While at it, move "numrows" processing out of the line of special cases,
and make it getopt's -r instead. (A similar thing could be done to
'conninfo', but current use of the program doesn't warrant spending time
on that -- nowhere else we use conninfo in so simplistic a manner.)

Discussion: https://postgr.es/m/20210401124850.GA19247@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/dde1a35aee6266dc8105717275335c46cd2b3650

Modified Files
--------------
src/test/modules/libpq_pipeline/libpq_pipeline.c | 32 +++++++++++-----------
.../modules/libpq_pipeline/t/001_libpq_pipeline.pl | 5 ++--
2 files changed, 18 insertions(+), 19 deletions(-)