ext/curl: Fix CURLOPT_PREREQFUNCTION to not continue on error conditions

[Ayesh]

This is a follow-up to GH-13255.

When the CURLOPT_PREREQFUNCTION callback does not return any value or return an invalid value, we throw a ValueError or a TypeError exception. However, it does not prevent the Curl request from going forward because our default return value is CURL_PREREQFUNC_OK.

This changes the default value to CURL_PREREQFUNC_ABORT.

[cmb69]

Thank you! Looks good to me; can we test this?

Somewhat related: #16513.

[Sjord]

Test:

--TEST--
CURLOPT_PREREQFUNCTION aborts transfer when callback throws
--EXTENSIONS--
curl
--SKIPIF--
<?php
if (!defined('CURLOPT_PREREQFUNCTION')) {
    die('skip CURLOPT_PREREQFUNCTION not available');
}
?>
--FILE--
<?php

include 'server.inc';
$host = curl_cli_server_start();
$ch = curl_init("{$host}/get.inc");

curl_setopt($ch, CURLOPT_PREREQFUNCTION,
    function (): int {
        throw new Exception('prereq failure');
    }
);

try {
    curl_exec($ch);
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}

var_dump(curl_errno($ch) === CURLE_ABORTED_BY_CALLBACK);

?>
--EXPECTF--
prereq failure
bool(true)