Description:
------------
SplTempFileObject::isReadable() and SplTempFileObject::isWritable() are returning false regardless the resource is readable or writable.

Test script:
---------------
$file = new \SplTempFileObject(-1);
$written = $file->fwrite('readable content');
$file->fflush();
$file->rewind();
var_dump($file->getFileInfo()->getPathname());
var_dump($file->valid());
var_dump($file->isReadable());
var_dump($file->fread($written));
var_dump($file->isWritable());
$written += $file->fwrite(' is writable');
$file->fflush();
$file->rewind();
var_dump($file->fread($written));

// @see https://3v4l.org/OEYn8

Expected result:
----------------
string(12) "php://memory"
bool(true)
bool(true)
string(16) "readable content"
bool(true)
string(28) "readable content is writable"

Actual result:
--------------
string(12) "php://memory"
bool(true)
bool(false)
string(16) "readable content"
bool(false)
string(28) "readable content is writable"