scd: avoid memory leaks

* scd/app-p15.c (send_certinfo): free labelbuf
  (do_sign): goto leave instead of return
* scd/command.c (cmd_genkey): goto leave instead of return

Modifified for this backport:

• scd/command.c (cmd_genkey): Make it easier to read by replacing

keyno with orig_line.

• Signed-off-by: Werner Koch <wk@gnupg.org>
• GnuPG-bug-id: T5393