patch 8.0.0073
Problem:    More comparisons between firstwin and lastwin.
Solution:   Use ONE_WINDOW for consistency. (Hirohito Higashi)
diff --git a/src/buffer.c b/src/buffer.c
index 8b1bceb..e5d2dde 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1412,7 +1412,7 @@
 # ifdef FEAT_AUTOCMD
 		   && !(curwin->w_closing || curwin->w_buffer->b_locked > 0)
 # endif
-		   && (firstwin != lastwin || first_tabpage->tp_next != NULL))
+		   && (!ONE_WINDOW || first_tabpage->tp_next != NULL))
 	{
 	    if (win_close(curwin, FALSE) == FAIL)
 		break;
@@ -5140,7 +5140,7 @@
 			: wp->w_width != Columns)
 		    || (had_tab > 0 && wp != firstwin)
 #endif
-		    ) && firstwin != lastwin
+		    ) && !ONE_WINDOW
 #ifdef FEAT_AUTOCMD
 		    && !(wp->w_closing || wp->w_buffer->b_locked > 0)
 #endif