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/eval.c b/src/eval.c
index 84a7b26..c43158a 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -5084,9 +5084,10 @@
     FOR_ALL_TAB_WINDOWS(tp, wp)
 	abort = abort || set_ref_in_item(&wp->w_winvar.di_tv, copyID,
 								  NULL, NULL);
-    if (aucmd_win != NULL)
-	abort = abort || set_ref_in_item(&aucmd_win->w_winvar.di_tv, copyID,
-								  NULL, NULL);
+    for (int i = 0; i < AUCMD_WIN_COUNT; ++i)
+	if (aucmd_win[i].auc_win_used)
+	    abort = abort || set_ref_in_item(
+		    &aucmd_win[i].auc_win->w_winvar.di_tv, copyID, NULL, NULL);
 #ifdef FEAT_PROP_POPUP
     FOR_ALL_POPUPWINS(wp)
 	abort = abort || set_ref_in_item(&wp->w_winvar.di_tv, copyID,