g10: Fix memory leak for PKT_signature.
* g10/getkey.c (buf_to_sig): Free by free_seckey_enc. * g10/gpgcompose.c (signature): Likewise. * g10/sign.c (write_signature_packets): Likewise.
- Reported-by: Philippe Antoine
- GnuPG-bug-id: T4047
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>