test_file_monitor_events() leaks an Error object when
qemu_file_monitor_add_watch() fails, which seems unlikely. Plug it.
Cc: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200630090351.1247703-11-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>