qapi: assert list entry has a value

This helps to figure out the expectations.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <20160930095948.3154-3-marcandre.lureau@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

qapi/qmp-input-visitor.c

@@ -84,6 +84,7 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv,
         assert(qobject_type(qobj) == QTYPE_QLIST);
         assert(!name);
         ret = qlist_entry_obj(tos->entry);
+        assert(ret);
         if (consume) {
             tos->entry = qlist_next(tos->entry);
         }