gpg: Allow no CRC24 checksum in armor.
* g10/armor.c (radix64_read): Detect the end of armor when there is no CRC24 checksum.
Cherry-pick master commit of:
3a344d6236521d768793e8b34a96a18ce13bab0e
- GnuPG-bug-id: T7071
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>