fix "missing initializer" warning

crypto/dso/dso_null.c

@@ -79,7 +79,8 @@ static DSO_METHOD dso_meth_null = {
 	NULL, /* dso_merger */
 	NULL, /* init */
 	NULL, /* finish */
-	NULL  /* pathbyaddr */
+	NULL, /* pathbyaddr */
+	NULL  /* globallookup */
 	};
 
 DSO_METHOD *DSO_METHOD_null(void)