ReadBits still drops bits on encountering the last byte

[itchyny]

This is quite similar to #6 but there is another failure case when Read() returns both data and io.EOF.
Here's a sample code.

• *myReader returns io.EOF with the last byte.
• Read with ReadBits(n >= 8) including the last byte.

package main

import (
	"fmt"
	"io"
	"os"

	bitstream "github.com/dgryski/go-bitstream"
)

type myReader struct {
	n int
}

func (e *myReader) Read(p []byte) (int, error) {
	switch e.n {
	case 0:
		p[0] = '\xF0'
		e.n++
		return 1, nil
	case 1:
		p[0] = '\x1F'
		e.n++
		return 1, io.EOF
	default:
		return 0, io.EOF
	}
}

func main() {
	br := bitstream.NewReader(&myReader{})
	b, err := br.ReadBits(4)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
		os.Exit(1)
	}
	fmt.Printf("%q\n", b)
	b, err = br.ReadBits(8)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
		os.Exit(1)
	}
	fmt.Printf("%q\n", b)
	b, err = br.ReadBits(4)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
	}
	fmt.Printf("%q\n", b)
	_, err = br.ReadBits(4)
	if err != io.EOF {
		panic("unreachable")
	}
}

The result is

'\x0f'
EOF
exit status 1

But, I expect the following output, no error.

'\x0f'
'\x01'
'\x0f'

[itchyny]

@dgryski Any thoughts?