Bail out early from internal_select() when socket file descriptor

closed.  Prevents core dump.

Modules/socketmodule.c

@@ -505,9 +505,14 @@ internal_select(PySocketSockObject *s, int writing)
 	fd_set fds;
 	struct timeval tv;
 
+	/* Nothing to do unless we're in timeout mode (not non-blocking) */
 	if (s->sock_timeout <= 0.0)
 		return;
 
+	/* Guard against closed socket */
+	if (s->sock_fd < 0)
+		return;
+
 	/* Construct the arguments to select */
 	tv.tv_sec = (int)s->sock_timeout;
 	tv.tv_usec = (int)((s->sock_timeout - tv.tv_sec) * 1e6);