Description:
------------
The option 'CURLOPT_FILE' takes a file handle as argument, however when you open the file read-only. cURL *silently* fails and downloads only 1 successful iteration of data.

This *only* happens when CURLOPT_RETURNTRANSFER is not defined, since that disables the 'CURLOPT_FILE' feature.

It's expected that some sort of warning/error is raised, just like when a write flag is set when the file is not writable. When the latter happens, cURL falls back on CURLOPT_RETURNTRANSFER = false.

Reproduce code:
---------------
<?php
error_reporting( E_ALL );

$ch = curl_init('http://kernel.org/pub/linux/kernel/v1.0/linux-1.0.tar.bz2');

$fp = fopen("/tmp/fubar", "r"); // Opening 'fubar' with the incorrect readonly flag
curl_setopt($ch, CURLOPT_FILE, $fp);
curl_exec($ch);

// Debug
$info = curl_getinfo($ch);

if ($info['size_download'] !== $info["download_content_length"]) {
        echo 'fail';
} else {
        echo 'works';
}

curl_close($ch);


Expected result:
----------------
works

Actual result:
--------------
fail