Description:
------------
preg_quote function escapes # character, while it shouldn't.

This breaks IPBoard 4.3.6 forums in which friendly urls uses custom regexes with #, @, ? characters in url templates. Urls are passed through preg_quote function and # is replaced with \#. In next section {#} should be replaced with (\d+), but this fails, since there is {#} but {\#}.


PHP 7.3.0-2 (cli) (built: Dec 17 2018 09:51:53) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.0-dev, Copyright (c) 1998-2018 Zend Technologies
    with Zend OPcache v7.3.0-2, Copyright (c) 1999-2018, by Zend Technologies

Test script:
---------------
<?php

        $inputs = ['#', '?', '@'];
        foreach($inputs as $input)
        {
                var_dump($input, preg_quote($input));
        }




Expected result:
----------------
string(1) "#"
string(1) "#"
string(1) "?"
string(2) "\?"
string(1) "@"
string(1) "@"

Actual result:
--------------
string(1) "#"
string(2) "\#"
string(1) "?"
string(2) "\?"
string(1) "@"
string(1) "@"