tests/qom-proplist: check duplicate "bv" property registration failed

"bv" is already a class property.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

tests/check-qom-proplist.c

@@ -125,10 +125,13 @@ static char *dummy_get_sv(Object *obj,
 
 static void dummy_init(Object *obj)
 {
+    Error *err = NULL;
+
     object_property_add_bool(obj, "bv",
                              dummy_get_bv,
                              dummy_set_bv,
-                             NULL);
+                             &err);
+    error_free_or_abort(&err);
 }