Previously, our helper script would read up to 4096 bytes and then re-open the
FIFO waiting for Kakoune to send another chunk. This was fine most of the time,
since who writes more than 4096 bytes interactively? Turns out, some people do,
and this left Kakoune hanging while it waited for a writer to show up and
receive the rest of the data.

Now, when we get a writer, we actually read and pass along all the data it has
for us, *then* close the handle and re-open it so we can wait for the next
chunk.# Please enter the commit message for your changes. Lines starting

Thanks to mıaomāı on Discord for pointing out this problem.