fix(grid): double grid_line_start() with ext_messages #31292

Problem:  Hit double grid_line_start() assert when redrawing from
          ext_messages msg_ruler event.
Solution: Do not start() batched grid calls when win_redr_ruler() will not
          puts() anything.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/nvim/drawscreen.c b/src/nvim/drawscreen.c
index 3719d38df2..19a8093a16 100644
--- a/src/nvim/drawscreen.c
+++ b/src/nvim/drawscreen.c
@@ -1092,9 +1092,13 @@ int showmode(void)
   win_T *ruler_win = curwin->w_status_height == 0 ? curwin : lastwin_nofloating();
   if (redrawing() && ruler_win->w_status_height == 0 && global_stl_height() == 0
       && !(p_ch == 0 && !ui_has(kUIMessages))) {
-    grid_line_start(&msg_grid_adj, Rows - 1);
+    if (!ui_has(kUIMessages)) {
+      grid_line_start(&msg_grid_adj, Rows - 1);
+    }
     win_redr_ruler(ruler_win);
-    grid_line_flush();
+    if (!ui_has(kUIMessages)) {
+      grid_line_flush();
+    }
   }
 
   redraw_cmdline = false;