htmlpurifier uses deprecated get_magic_quotes_gpc

[edgreenberg]

PHP 7.4 threw a deprecation error on one of my uses of get_magic_quotes_gpc(). When I searched the code to see where else it was used, I found it on library/HTMLPurifier/Config.php:806 (version 4.13.0).

I didn't get the error on HTMLPurifier, so this is just a courtesy notice.

See https://stackoverflow.com/questions/61054418/php-7-4-deprecated-get-magic-quotes-gpc-function-alternative

Thank you

[thelem]

Fixed in #273