AsyncProc crashes when multiple processes are started

[antoinets]

This chain of events leads to a crash:

1. Async process p1 started.
2. Async process p2 started.
3. Async process p1 finishes, and the crash happens here.

Small example:

import asyncdispatch, asynctools/asyncproc

proc run() {.async.} =
  while true:
    await sleepAsync(300)
    var p = startProcess("sleep 1 && ls", options={poUsePath, poEvalCommand})
    asyncCheck p.waitForExit()

waitFor run()

Which gives the error:

Error: unhandled exception: Resource temporarily unavailable (code: 11) [IOSelectorsException]