uv_fs_close on an unexisting stream doesn't return an error

Looks like uv_fs_close always returns the initial stream, even when this stream doesn't exist and close fails.

For example, 

``` php
uv_fs_close($loop, 42, function ($result){});
```

returns 42

``` php
uv_fs_close($loop, 0, function ($result){});
```

returns 0, and so on.
