Description:
------------
In a filter_callback function, if the function return false, the system crash, the apache hange.

if return other things other than false, for example 'aaa',true,1, it works

Reproduce code:
---------------
function returnTrue($val){
    return true;
}

function returnFalse($val){
    return false;
}

var_dump(filter_var('aaaa', FILTER_CALLBACK, array("options"=>"returnTrue")));

var_dump(filter_var('aaaa', FILTER_CALLBACK, array("options"=>"returnFalse")));

Expected result:
----------------
bool(true)
bool(false)

Actual result:
--------------
nothing can see, because the system crashed