gpg: Fix searching for mail addresses in keyrings.

gpg: Fix searching for mail addresses in keyrings.

* g10/keyring.c (compare_name): Fix KEYDB_SEARCH_MODE_MAIL* searches
in keyrings when the UID is a plain addr-spec.
--
Previously, 'gpg --list-key "<foo@example.org>"' failed if 1/ the
keyring format is used and 2/ the key's UID is a plain addr-spec
(cf. RFC2822 section 4.3), e.g. 'foo@example.org'.

GnuPG-bug-id: 2930
Signed-off-by: Justus Winter <justus@g10code.com>
(cherry picked from commit 3f4f20ee6eff052c88647b820d9ecfdbd8df0f40)

Gbp-Pq: Name 0018-gpg-Fix-searching-for-mail-addresses-in-keyrings.patch