Fix bulk action handling incompatibility

"handle_bulk_actions-edit-shop_order" is a filter, which should return a value, not just null, because other plugins might customized it already. This causes issues, like showing a white screen instead of handling the bulk action.

Author: passatgt

includes/class-wcdn-writepanel.php

@@ -134,11 +134,11 @@ public function register_my_bulk_actions( $bulk_actions ) {
 		public function my_bulk_action_handler( $redirect_to, $doaction, $post_ids ) {
 			// stop if there are no post ids.
 			if ( ! isset( $_REQUEST['post'] ) ) {
-				return;
+				return $redirect_to;
 			}
 			// stop if the action is not of bulk printing.
 			if( ! in_array( $_REQUEST['action'], array( 'wcdn_print_invoice', 'wcdn_print_delivery-note', 'wcdn_print_receipt' ) ) ) {
-				return;
+				return $redirect_to;
 			}
 			// only for specified actions.
 			foreach ( WCDN_Print::$template_registrations as $template_registration ) {
@@ -149,15 +149,15 @@ public function my_bulk_action_handler( $redirect_to, $doaction, $post_ids ) {
 				}
 			}
 			if ( ! isset( $report_action ) ) {
-				return;
+				return $redirect_to;
 			}
 
 			// security check.
 			check_admin_referer( 'bulk-posts' );
 
 			// get referrer.
 			if ( ! wp_get_referer() ) {
-				return;
+				return $redirect_to;
 			}
 
 			// filter the referer args.