gpg: Ignore too large user ids during import.

* g10/import.c (read_block): Add special treatment for bad user ids
and comment packets.

See
for an example of a bogus user id.

(cherry picked from commit 01cd66f9faf1623833e6afac84164de5a136ecff)

• GnuPG-bug-id: T4022
• Signed-off-by: Werner Koch <wk@gnupg.org>