Description:
------------
Surrogate codepoints cannot be validly encoded in UTF-8. Iconv should return false when given a byte sequence that would encode them and an in_charset of 'UTF-8'.

This works as expected on Linux https://3v4l.org/Ff6cr but doesn't on Windows (tested with PHP 7.0.16 and 7.1.2.)

Test script:
---------------
$high = "\xED\xa1\x92"; // codepoint D852
$low = "\xED\xBD\xA2"; // codepoint DF62
$pair = $high.$low;
var_dump(
    @\iconv('UTF-8', 'UTF-8', $high) === false,
    @\iconv('UTF-8', 'UTF-8', $low) === false,
    @\iconv('UTF-8', 'UTF-8', $pair) === false
);

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

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