Description:
------------
Recently, the stream_set_read_buffer() was introduced; it's signature suggests that a buffer size can be set.

However, when passing any non-zero value, the stream becomes unbuffered.

This is because of a missing check inside _php_stream_set_option():

if (value == PHP_STREAM_BUFFER_NONE) {
    stream->flags |= PHP_STREAM_FLAG_NO_BUFFER;
} else {
    stream->flags ^= PHP_STREAM_FLAG_NO_BUFFER;
}

Test script:
---------------
<?php

$f = fopen('/dev/urandom', 'rb');
// setting read buffer to 1024
stream_set_read_buffer($f, 1024);
// reading the first 10 bytes
$s = fread($f, 10);
fclose($f);

/*
========= STRACE OUTPUT =========

open("/dev/urandom", O_RDONLY)          = 3
fstat64(3, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 9), ...}) = 0
lseek(3, 0, SEEK_CUR)                   = 0
read(3, "\3X\264\rQ\277\273\367\347Z", 10) = 10
close(3)                                = 0
*/
?>

Expected result:
----------------
Either the read() loads 1024 bytes, which would be ideal, or it should still load the default buffer size (8192 bytes).

The attached patch addresses the latter behaviour.