When I use FrameEncoder, the last part of the file is not actually written properly:

let output = Box::new(lz4_flex::frame::FrameEncoder::new(File::create(output)?));
// many write calls
output.flush()?;

Using lz4cat on resulting file gives Error 68: unfinished stream.

I need this boxing because I am generalizing multiple output backends with Box<dyn Write>. I am not sure if this is causing the issue here, but flate2 with its gzip decoder closes files properly.