ITS#7451 fix back-ldif return on empty dir

Broken by commit 2d1af3f2

servers/slapd/back-ldif/ldif.c

@@ -1780,7 +1780,7 @@ ldif_tool_entry_first_x( BackendDB *be, struct berval *base, int scope, Filter *
 		op.ors_scope = LDAP_SCOPE_SUBTREE;
 		if ( search_tree( &op, NULL ) != LDAP_SUCCESS ) {
 			tl->ecurrent = tl->ecount; /* fail ldif_tool_entry_next() */
-			return 0; /* fail ldif_tool_entry_get() */
+			return NOID; /* fail ldif_tool_entry_get() */
 		}
 	}
 	return ldif_tool_entry_next( be );