Fix underline rendering

src/ui_model/line.rs

@@ -158,10 +158,6 @@ impl Line {
         self.item_line[start_cell] = Some(Item::new(new_item.clone(), end_cell - start_cell + 1));
     }
 
-    pub fn mark_dirty_cell(&mut self, idx: usize) {
-        self.line[idx].dirty = true;
-    }
-
     pub fn get_item_mut(&mut self, cell_idx: usize) -> Option<&mut Item> {
         let item_idx = self.cell_to_item(cell_idx);
         if item_idx >= 0 {

src/ui_model/mod.rs

@@ -74,13 +74,13 @@ impl UiModel {
         let mut changed_region = self.cur_point();
         let line = &mut self.model[self.cur_row];
         line.dirty_line = true;
-        line.mark_dirty_cell(self.cur_col);
 
         let cell = &mut line[self.cur_col];
 
         cell.ch = text.chars().last().unwrap_or(' ');
         cell.attrs = attrs.map(Attrs::clone).unwrap_or_else(Attrs::new);
         cell.attrs.double_width = text.is_empty();
+        cell.dirty = true;
         self.cur_col += 1;
         if self.cur_col >= self.columns {
             self.cur_col -= 1;