Infinite loop after decoding error

[jongiddy]

Similar to behavior in #96 but different enough to warrant its own issue. Notably #97 does not fix this problem.

After a decoding error try_finish goes into an infinite loop:

#[test]
fn write_invalid() {
    let contents = b"BZh\xfb";
    let mut decoder = bzip2::write::BzDecoder::new(Vec::new());
    dbg!(decoder.write(&contents[..]));
    dbg!(decoder.try_finish());
}

I'm explicitly calling try_finish here to show the problem. But since the Drop implementation calls try_finish this cannot be avoided by not calling try_finish.