Description:
------------
The filter extension considers "0x" and "0X" valid hexadecimal numbers when passed through the FILTER_VALIDATE_INT filter with the FILTER_FLAG_ALLOW_HEX flag.

Test script:
---------------
https://3v4l.org/m1Pnc

<?php

var_dump(filter_var('0x', FILTER_VALIDATE_INT, FILTER_FLAG_ALLOW_HEX));
var_dump(filter_var('0X', FILTER_VALIDATE_INT, FILTER_FLAG_ALLOW_HEX));
var_dump(filter_var('', FILTER_VALIDATE_INT, FILTER_FLAG_ALLOW_HEX));
var_dump(filter_var('0', FILTER_VALIDATE_INT, FILTER_FLAG_ALLOW_HEX));

Expected result:
----------------
bool(false)
bool(false)
bool(false)
int(0)

Actual result:
--------------
int(0)
int(0)
bool(false)
int(0)