patch 8.0.0073
Problem:    More comparisons between firstwin and lastwin.
Solution:   Use ONE_WINDOW for consistency. (Hirohito Higashi)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index dcb5cfe..9ad7d77 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -7488,9 +7488,9 @@
 {
     /* First close all the windows but the current one.  If that worked then
      * close the last window in this tab, that will close it. */
-    if (lastwin != firstwin)
+    if (!ONE_WINDOW)
 	close_others(TRUE, forceit);
-    if (lastwin == firstwin)
+    if (ONE_WINDOW)
 	ex_win_close(forceit, curwin, NULL);
 # ifdef FEAT_GUI
     need_mouse_correct = TRUE;