gpg: Find keys using mail addresses with garbage after the '>'

* kbx/keybox-search.c (blob_cmp_mail): Stop comparing at the '>'.

This change allows to find mail addresses like

Joe Doe <joe@example.org> bar
Joe Doe <joe@example.org> (comment)

using the command

gpg  -k '<joe@example.org'

or (with syntactic sugar)

gpg  -k '<joe@example.org>'

These UIDs are ill-formed according to gpg checks but nevertheless are
seen in the wild.

Note, that it does only work with the new keybox format.

• Signed-off-by: Werner Koch <wk@gnupg.org>