qapi: Add test for nonexistent schema file

This tests the error-return pathway introduced in the previous commit.
(Thanks to Paolo for the help with the Meson magic.)

Signed-off-by: John Snow <jsnow@redhat.com>

Message-Id: <20210519183951.3946870-3-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
3 files changed