fix bug: missing structure entry

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@6932 57a11ea4-9604-0410-9ed3-97b8803252fd

src/engine/test/test-object.c

@@ -24,6 +24,7 @@ static GncObject_t bus_obj = {
   NULL,				/* create */
   NULL,				/* destroy */
   NULL,                         /* is dirty */
+  NULL,				/* mark_clean */
   foreach,
   printable,
 };