qapi: Fix the virtual walk example in visitor.h's big comment

Call visit_check_list().  Missed in commit a4a1c70dc7 "qapi: Make
input visitors detect unvisited list tails".

Drop an irrelevant error_propagate() while there.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200424084338.26803-3-armbru@redhat.com>
1 file changed