Actually fix gpgme segfault in create_recipient_set().

Actually fix gpgme segfault in create_recipient_set().

Changeset 6e44bfa16096 did not fix the segv.  (Sorry, I made the fix
based off a report on IRC but didn't trigger the segv myself: it was
caused by an out-of-tree patch).

The actual problem was that the rset was only resized on a successful
gpgme_get_key().  However, on error, the array still needs to be
NULL-terminated before calling free_recipient_set().

Move the resize so it always takes place.  This obviates the need for
the NULL check added in 6e44bfa16096.