asyncio: BaseSubprocessTransport._kill_wait() now also call close()

close() closes pipes, which is not None yet by _kill_wait().

Lib/asyncio/base_subprocess.py

@@ -117,12 +117,15 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
             proc.stderr.close()
         if proc.stdin:
             proc.stdin.close()
+
         try:
             proc.kill()
         except ProcessLookupError:
             pass
         self._returncode = proc.wait()
 
+        self.close()
+
     @coroutine
     def _post_init(self):
         try: