patch 9.0.0206: redraw flags are not named specifically

Problem:    Redraw flags are not named specifically.
Solution:   Prefix "UPD_" to the flags, for UPDate_screen().
diff --git a/src/undo.c b/src/undo.c
index 924108c..3b35452 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3038,7 +3038,7 @@
 	FOR_ALL_WINDOWS(wp)
 	{
 	    if (wp->w_buffer == curbuf && wp->w_p_cole > 0)
-		redraw_win_later(wp, NOT_VALID);
+		redraw_win_later(wp, UPD_NOT_VALID);
 	}
     }
 #endif