Fix panic in From<io::Error> implementation for frame::Error

[phoerious]

The From implementation for converting an io::Error to a frame::Error always panics for custom IO errors.

This is the current implementation:

impl From<io::Error> for Error {
    fn from(e: io::Error) -> Self {
        match e.get_ref().map(|e| e.downcast_ref::<Error>()) {
            Some(_) => *e.into_inner().unwrap().downcast::<Error>().unwrap(),
            None => Error::IoError(e),
        }
    }
}

This will always panic on the last unwrap() for any kind of custom IO error that is not a wrapped frame::Error, regardless of whether e.downcast_ref::<Error>() actually succeeded.

I changed the map() call to and_then(), which is probably the originally intended behaviour.

Found this bug while testing error propagation in my own LZ4 stream wrapper implementation, which uses lz4_flex as a backend.

[PSeitz]

Thanks for the fix!

[PSeitz]

released in 0.13.1