filter.js generates incorrect URL when “Use full friendly URLs” is enabled

[Painbaker]

Affected version

2.3.7

When using filter.js on the public interface with AJAX filtering and the “Use full friendly URLs” option enabled, the generated request URL is incorrect. It misses a ? before the query string, which results in an invalid URL.

/forum-search/&_xfFilter[text]=test&_xfFilter[prefix]=0?_xfResponseType=json&_xfWithData=1&_xfRequestUri=/&_xfToken=1752795635,ed211239fc7c29d2bfdacd66aecf7ca10

When expected

/forum-search/?_xfFilter[text]=test&_xfFilter[prefix]=0?_xfResponseType=json&_xfWithData=1&_xfRequestUri=/&_xfToken=1752795635,ed211239fc7c29d2bfdacd66aecf7ca10

In filter.js, the URL is built by concatenating parameters using + '&' + params, regardless of whether the base AJAX URL contains a query string or not:

    _filterAjax (text, prefix)
        {
            //  
            if (!text.length)
            {
                this._clearAjaxRows()
                const matched = this._applyFilter(this._getSearchRows(), text, prefix)
                this._toggleNoResults(matched == 0)
            }
            else
            {
                const params = Object.entries({
                    text,
                    prefix: prefix ? 1 : 0,
                }).map(([key, value]) => `_xfFilter[${key}]=${encodeURIComponent(value)}`).join('&')

                const ajaxUrl = this.options.ajax + '&' + params // <--
                //
            }
        },