gnupg: apply patch to allow import of key updates without user ids

This adds a patch series which allows GnuPG to import updates
(revocations and subkeys) from certificates that contain no user ids.
This is relevant for refreshing keys from the default keyserver
keys.openpgp.org, where only user ids that contain verified email
addresses will be distributed, and revoked keys never contain any user
ids.

This patch series was originally authored and submitted to upstream half
a year ago (by me), but now comes from Debian packaging where it's been
included since then.

Relates to the following upstream issue: https://dev.gnupg.org/T4393