Multiple long lasting connections fail
The code below works fine for a single connected client. As soon as a second client connects the first one gets no data any more. The data intended for the first client and the data for the second client all go to the second client.
The fist client stays connected but receives nothing.
(An as similar as possible setup with the standard asynchttpserver works flawless.)

Nim 1.4.8 [Windows: amd64] Win10

```
import asyncnet, os, strformat
import prologue

proc genNumbers(): auto =
  var n = 0
  return iterator: int =
    while true:
      yield n
      inc(n)

proc sse(ctx: Context) {.async.} =
  let dataGenerator = genNumbers()
  let headers = {
    "Access-Control-Allow-Origin": "*",
    "Cache-Control": "no-cache", 
    "Content-type": "text/event-stream", 
    "Connection": "keep-alive",
    "Content-Length": ""
  }
  await ctx.respond(Http200, "", headers.initResponseHeaders())
  while true:
    echo "socket handle : ", int(ctx.request.nativeRequest.client.getFD)
    let n = dataGenerator()
    let data = "data: n = {n}\n\n".fmt
    await ctx.send(data)
    await sleep_async(2000)

let
  env = loadPrologueEnv(".env")
  settings = newSettings(
    debug = true,
    address = env.getOrDefault("address", "192.168.1.4"),
    port = Port(env.getOrDefault("port", 8088)),
    #reusePort = false
  )

var app = newApp(settings = settings)
app.addRoute("/sse", sse, HttpGet)
app.run()
```

Python3 client to listen to the event stream:
```
import urllib.request

req = urllib.request.Request(
    'http://192.168.1.4:8088/sse/',
    method='GET'
)

#url = 'http://192.168.1.4:8088/sse/'
with urllib.request.urlopen(req) as response:
    print (response.url)
    print (response.headers)
    print (response.status)
    for line in response:
        print(line)
```