g10: Fix memory leak.
* g10/import.c (read_block): Call free_packet to skip the packet.
Cherry-pick of master commit of:
7c96cc67e108f3a9514a4222ffac2f9f9a2ab19e
- Reported-by: Philippe Antoine
- GnuPG-bug-id: T3916
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>