Add test for issue #4757

tests/async/tasyncsend4757.nim

@@ -0,0 +1,16 @@
+discard """
+  file: "tasyncsend4754.nim"
+  output: "Finished"
+"""
+
+import asyncdispatch
+
+proc f(): Future[void] {.async.} =
+  let s = newAsyncNativeSocket()
+  await s.connect("example.com", 80.Port)
+  await s.send("123")
+  echo "Finished"
+
+asyncCheck f()
+
+poll(1000)