Arguments of 'pin' subcommand should be checked
at the very beginning of do_pin_any().
Otherwise segfault errors can occur when using
'map pin' or 'prog pin' commands, so fix it.

  # bpftool prog pin id
  Segmentation fault

Fixes: 71bb428f ("tools: bpf: add bpftool")
Reviewed-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reported-by: NTaehee Yoo <ap420073@gmail.com>
Signed-off-by: NTaeung Song <treeze.taeung@gmail.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>