Fix Windows accept() to fail future instead of raising

Resolves: #5279

tests/async/tacceptcloserace.nim

@@ -0,0 +1,29 @@
+import asyncdispatch, net, os, nativesockets
+
+# bug: https://github.com/nim-lang/Nim/issues/5279
+
+proc setupServerSocket(hostname: string, port: Port): AsyncFD =
+  let fd = newNativeSocket()
+  setSockOptInt(fd, SOL_SOCKET, SO_REUSEADDR, 1)
+  var aiList = getAddrInfo(hostname, port)
+  if bindAddr(fd, aiList.ai_addr, aiList.ai_addrlen.Socklen) < 0'i32:
+    freeAddrInfo(aiList)
+    raiseOSError(osLastError())
+  freeAddrInfo(aiList)
+  if listen(fd) != 0:
+    raiseOSError(osLastError())
+  setBlocking(fd, false)
+  result = fd.AsyncFD
+  register(result)
+
+const port = Port(5614)
+for i in 0..100:
+  let serverFd = setupServerSocket("localhost", port)
+  serverFd.accept().callback = proc(fut: Future[AsyncFD]) =
+    if not fut.failed:
+      fut.read().closeSocket()
+
+  var fd = newAsyncNativeSocket()
+  waitFor fd.connect("localhost", port)
+  serverFd.closeSocket()
+  fd.closeSocket()