fix: fix proactor transport for windows

Author: ordinary-jamie

Lib/asyncio/proactor_events.py

@@ -63,7 +63,11 @@ def __init__(self, loop, sock, protocol, waiter=None,
         self._called_connection_lost = False
         self._eof_written = False
         if self._server is not None:
-            self._server._attach(self)
+            if self._server.is_serving():
+                self._server._attach(self)
+            else:
+                self.abort()
+                return
         self._loop.call_soon(self._protocol.connection_made, self)
         if waiter is not None:
             # only wake up the waiter when connection_made() has been called