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/digraph.c b/src/digraph.c
index f37292f..de4ff83 100644
--- a/src/digraph.c
+++ b/src/digraph.c
@@ -2025,8 +2025,10 @@
 	ui_breakcheck();
 	++dp;
     }
-    must_redraw = CLEAR;    // clear screen, because some digraphs may be
-			    // wrong, in which case we messed up ScreenLines
+
+    // clear screen, because some digraphs may be wrong, in which case we
+    // messed up ScreenLines
+    must_redraw = UPD_CLEAR;
 }
 
     static void