[regression] vibe looses static file requests

[MartinNowak]

Reproduce by creating a file that is bigger than 4096 bytes and requesting it with 2 concurrent connections.

#!/bin/sh
DIR=`mktemp -d`/serve
dub init "$DIR" vibe.d
pushd "$DIR"
sed -i 's|"vibe.*>=0.*"|"vibe-d": "~master"|' package.json
cat > source/app.d << CODE
import vibe.d;

shared static this()
{
    auto settings = new HTTPServerSettings;
    settings.port = 8080;

    listenHTTP(settings, serveStaticFiles("."));
}
CODE
dub build
# create a file that is bigger than 4096 bytes
dd if=/dev/zero of=foobar count=1 bs=4097
./serve &
PID=$!
# wait for serve
sleep 1
# second ab request times out after 5 seconds
ab -s 5 -n 2 -c 2 http://localhost:8080/foobar
kill $PID
popd
rm -r "$DIR"

[MartinNowak]

Bisecting points to this commit c5a9025.