fix for https://github.com/Automattic/woocommerce-subscriptions-core/ Site crashes with out of memory error when adding a downloadable product and hitting Update button

woo-subscr-fix.php

// file:
    ///plugins/woocommerce-subscriptions/vendor/woocommerce/subscriptions-core/includes/class-wcs-download-handler.php

    /**
     * Grant downloadable file access to any newly added files on any existing subscriptions
     * which don't have existing permissions pre WC3.0 and all subscriptions post WC3.0.
     *
     * @param int $product_id
     * @param int $variation_id
     * @param array $downloadable_files product downloadable files
     * @since 1.0.0 - Migrated from WooCommerce Subscriptions v2.0.18
     */
    public static function grant_new_file_product_permissions( $product_id, $variation_id, $downloadable_files ) {
        if ( wcs_is_woocommerce_pre( '3.0' ) ) {
            return;
        }

        global $wpdb;

        $product_id            = !empty($variation_id) ? $variation_id : $product_id;
        $product               = wc_get_product( $product_id );
        $existing_download_ids = array_keys( (array) wcs_get_objects_property( $product, 'downloads' ) );
        $downloadable_ids      = array_keys( (array) $downloadable_files );
        $new_download_ids      = array_filter( array_diff( $downloadable_ids, $existing_download_ids ) );

        if ( empty( $new_download_ids ) ) {
            return;
        }

        $subscriptions = wcs_get_subscriptions_for_product( $product_id );

        if ( empty( $subscriptions ) ) { // No subscriptions
            return;
        }

        foreach ( $subscriptions as $subscription_id ) {
            // $subscription_id is technically an order id for a subscription product
            $permission_by_order_id = $wpdb->get_var(
                $wpdb->prepare( "SELECT order_id FROM {$wpdb->prefix}woocommerce_downloadable_product_permissions WHERE order_id = %d AND product_id = %d LIMIT 1",
                    $subscription_id, $product_id
                )
            );

            if ( empty( $permission_by_order_id ) ) {
                continue;
            }

            $subscription = wcs_get_subscription( $subscription_id );

            if ( empty( $subscription ) ) {
                continue;
            }

            foreach ( $new_download_ids as $download_id ) {
                // WooCommerce generates random IDs and this is almost pointless.
                // I used the debugger and stopped the debugging session right after wc_downloadable_file_permission() was called.
                $permission_found = $wpdb->get_var(
                    $wpdb->prepare( "SELECT download_id FROM {$wpdb->prefix}woocommerce_downloadable_product_permissions
                             WHERE order_id = %d AND product_id = %d AND download_id = %s LIMIT 1",
                        $subscription_id, $product_id, $download_id
                    )
                );

                if ( ! empty( $permission_found ) ) {
                    continue;
                }

                // Grant permissions to subscriptions which have no permissions for this product, pre WC3.0, or all subscriptions, post WC3.0, as WC doesn't grant them retrospectively anymore.
                if ( apply_filters( 'woocommerce_process_product_file_download_paths_grant_access_to_new_file', true, $download_id, $product_id, $subscription ) ) {
                    wc_downloadable_file_permission( $download_id, $product_id, $subscription );
                }
            }
        }
    }