Undefined variable $ajax_delay_ms in …/wpsolr_include.inc.php

PHP Warning: Undefined variable $ajax_delay_ms in /var/www/html/wp-content/plugins/wpsolr-free/wpsolr/core/wpsolr_include.inc.php on line 740

Seems like the $ajax_delay_ms value isn’t always set at runtime.

Fixed temporarily with

                if (!isset($ajax_delay_ms)) {
                        $ajax_delay_ms = 500;
                }

Added at line ~715