patch 8.0.0956: scrolling in a terminal window has flicker

Problem:    Scrolling in a terminal hwindow as flicker when the Normal
            background differs from the terminal window background.
Solution:   Set the attribute to clear with.
diff --git a/src/move.c b/src/move.c
index f058b73..a5ba011 100644
--- a/src/move.c
+++ b/src/move.c
@@ -1163,7 +1163,7 @@
 	if (extra > 0)
 	    win_ins_lines(curwin, 0, extra, FALSE, FALSE);
 	else if (extra < 0)
-	    win_del_lines(curwin, 0, -extra, FALSE, FALSE);
+	    win_del_lines(curwin, 0, -extra, FALSE, FALSE, 0);
     }
     else
 	curwin->w_skipcol = 0;