patch 8.2.1059: crash when using :tabonly in an autocommand

Problem:    Crash when using :tabonly in an autocommand. (Yegappan Lakshmanan)
Solution:   Do not allow the autocommand window to be closed.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 6c887fa..2469df3 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -5178,6 +5178,13 @@
     int		need_hide;
     buf_T	*buf = win->w_buffer;
 
+    // Never close the autocommand window.
+    if (win == aucmd_win)
+    {
+	emsg(_(e_autocmd_close));
+	return;
+    }
+
     need_hide = (bufIsChanged(buf) && buf->b_nwindows <= 1);
     if (need_hide && !buf_hide(buf) && !forceit)
     {