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/misc2.c b/src/misc2.c
index c5149ff..e17a6f1 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -719,7 +719,7 @@
 
     if (retval)
 	curwin->w_set_curswant = TRUE;
-    redraw_later(NOT_VALID);
+    redraw_later(UPD_NOT_VALID);
     return retval;
 }