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