Fix #6.

Add tests for #6.

tests/testbugs.nim

@@ -0,0 +1,42 @@
+#              Asyncdispatch2 Test Suite
+#                 (c) Copyright 2018
+#         Status Research & Development GmbH
+#
+#              Licensed under either of
+#  Apache License, version 2.0, (LICENSE-APACHEv2)
+#              MIT license (LICENSE-MIT)
+
+import unittest
+import ../asyncdispatch2
+
+const HELLO_PORT = 45679
+const TEST_MSG = "testmsg"
+const MSG_LEN = TEST_MSG.len()
+
+type
+  CustomData = ref object
+    test: string
+
+proc udp4DataAvailable(transp: DatagramTransport,
+                     remote: TransportAddress): Future[void] {.async, gcsafe.} =
+  var udata = getUserData[CustomData](transp)
+  if udata.test == "CHECK":
+    udata.test = "OK"
+  transp.close()
+
+proc issue6(): Future[bool] {.async.} =
+  var myself = initTAddress("127.0.0.1:" & $HELLO_PORT)
+  var data = CustomData()
+  data.test = "CHECK"
+  var dsock4 = newDatagramTransport(udp4DataAvailable, udata = data,
+                                    local = myself)
+  await dsock4.sendTo(myself, TEST_MSG, MSG_LEN)
+  await dsock4.join()
+  if data.test == "OK":
+    result = true
+
+when isMainModule:
+  suite "Asynchronous issues test suite":
+    test "Issue #6":
+      var res = waitFor(issue6())
+      check res == true