Bug: default Read::read_to_end panic after seek

[KKould]

before fix:

fn read_to_end(
        &mut self,
        mut buf: Vec<u8>,
    ) -> impl Future<Output = Result<Vec<u8>, Error>> + MaybeSend {
        async move {
            buf.resize(self.size().await? as usize, 0);
            let buf = self.read_exact(buf).await?;
            Ok(buf)
        }
    }

When Seek is not 0, resizing buf to the full size of the file results in eof