patch 9.0.0965: using one window for executing autocommands is insufficient

Problem:    Using one window for executing autocommands is insufficient.
Solution:   Use up to five windows for executing autocommands.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index bb4a831..218b7ed 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -6050,7 +6050,7 @@
     buf_T	*buf = win->w_buffer;
 
     // Never close the autocommand window.
-    if (win == aucmd_win)
+    if (is_aucmd_win(win))
     {
 	emsg(_(e_cannot_close_autocmd_or_popup_window));
 	return;