win: reset pipe handle for pipe servers

On pipe servers handle->handle takes turns between the different server
handles, so after closing all of them just reset the dandling reference.

PR-URL: https://github.com/libuv/libuv/pull/488
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/win/pipe.c

@@ -748,6 +748,7 @@ void uv_pipe_cleanup(uv_loop_t* loop, uv_pipe_t* handle) {
         handle->pipe.serv.accept_reqs[i].pipeHandle = INVALID_HANDLE_VALUE;
       }
     }
+    handle->handle = INVALID_HANDLE_VALUE;
   }
 
   if (handle->flags & UV_HANDLE_CONNECTION) {