fix #13132 tnetdial (#13318)

Author: timotheecour

tests/stdlib/tnetdial.nim

@@ -2,7 +2,6 @@ discard """
  cmd: "nim c --threads:on $file"
  exitcode: 0
  output: "OK"
- disabled: "travis"
 """
 
 import os, net, nativesockets, asyncdispatch
@@ -39,10 +38,10 @@ proc testThread() {.thread.} =
  fd.close()
 
 proc test() =
+ let serverFd = initIPv6Server("::1", port)
  var t: Thread[void]
  createThread(t, testThread)
 
- let serverFd = initIPv6Server("::1", port)
  var done = false
 
  serverFd.accept().callback = proc(fut: Future[AsyncFD]) =
@@ -58,4 +57,5 @@ proc test() =
 
  joinThread(t)
 
+# this would cause #13132 `for i in 0..<10000: test()`
 test()