Description:
------------
Sometimes I experience that stream_get_contents never completes executing

In this case a PDF file is processed via poppler's pdftops. The PDF contains some errors though but when running the command directly in a terminal it completes and returns

The code only prints "opened" but never reach "ouput done"

The PDF can be found here
https://docdro.id/fHlIxBS

Test script:
---------------
$syntax = '/var/bin/poppler-0.79.0/build/utils/pdftops file.pdf file.ps';

$pipes = [];
$process = proc_open($syntax, [
	0 => ['pipe', 'r'],	// stdin
	1 => ['pipe', 'w'],	// stdout
	2 => ['pipe', 'w']	// stderr
], $pipes);
fclose($pipes[0]);

echo "opened\n";

$output 	= stream_get_contents($pipes[1]);
echo "output done\n";
$stderr 	= stream_get_contents($pipes[2]);
echo "err done\n";

foreach($pipes as $pipe){
	if(is_resource($pipe)){
		fclose($pipe);
	}
}

$exitcode = proc_close($process);

echo "err: $stderr\n";
echo "out: $output\n";

Expected result:
----------------
opened
output done
err done
err:
output:

Actual result:
--------------
opened