patch 9.0.0245: mechanism to prevent recursive screen updating is incomplete

Problem:    Mechanism to prevent recursive screen updating is incomplete.
Solution:   Add "redraw_not_allowed" and set it in build_stl_str_hl().
            (issue #10952)

src/screen.c

@@ -2906,7 +2906,7 @@ give_up:
     screen_Rows = Rows;
     screen_Columns = Columns;
 
-    must_redraw = UPD_CLEAR;	// need to clear the screen later
+    set_must_redraw(UPD_CLEAR);	// need to clear the screen later
     if (doclear)
 	screenclear2();
 #ifdef FEAT_GUI