patch 8.0.1100: stuck in redraw loop when 'lazyredraw' is set

Problem:    Stuck in redraw loop when 'lazyredraw' is set.
Solution:   Don't loop on update_screen() when not redrawing. (Yasuhiro
            Matsumoto, closes #2082)
diff --git a/src/proto/screen.pro b/src/proto/screen.pro
index b40e0da..39424b4 100644
--- a/src/proto/screen.pro
+++ b/src/proto/screen.pro
@@ -10,7 +10,7 @@
 void redraw_after_callback(int call_update_screen);
 void redrawWinline(linenr_T lnum, int invalid);
 void update_curbuf(int type);
-void update_screen(int type_arg);
+int update_screen(int type_arg);
 int conceal_cursor_line(win_T *wp);
 void conceal_check_cursur_line(void);
 void update_single_line(win_T *wp, linenr_T lnum);