### Godot version

4.0 beta 10

### System information

Windows 11 Vulkan

### Issue description

Looked through the issues list, but couldn't find something like this, sorry in advance if this has already been reported.

There is a few cases (in the pictures below) where list of Actions in Input Map may not always show a scrollbar even if the actions list overflows (I imagine this could also happen for the widget that Input Map uses).

![image](https://user-images.githubusercontent.com/39958198/210003566-cf60dbaf-921f-485b-b0a9-51ffc28d0244.png)

![New Bitmap image](https://user-images.githubusercontent.com/39958198/210004079-8eb2e6a1-0cf5-4a7c-8905-a4e3cfd0ec5d.png)

![image](https://user-images.githubusercontent.com/39958198/210004165-a6b6790b-248a-4f68-b4d0-b44b25afdf4f.png)

![image](https://user-images.githubusercontent.com/39958198/210004537-aca52194-a464-48b9-b818-24782706de45.png)


### Steps to reproduce

The pictures are clearer than anything I could write here: "a picture is worth 1000 words"

### Minimal reproduction project

N/A
if (theme_cache.draw_relationship_lines == 0) {
					return -1; 
				}
				htotal = -1;
				children_pos.y = theme_cache.offset.y + p_draw_size.height;
			} else {
				htotal += child_h;
				children_pos.y += child_h;
			}
			c = c->next;
		}
	}
	return htotal;
}
int Tree::_count_selected_items(TreeItem *p_from) const {
	int count = 0;
	for (int i = 0; i < columns.size(); i++) {
		if (p_from->is_selected(i)) {
			count++;
		}
	}
	if (p_from->get_first_child()) {
		count += _count_selected_items(p_from->get_first_child());
	}
	if (p_from->get_next()) {
		count += _count_selected_items(p_from->get_next());
	}
	return count;
}
bool Tree::_is_branch_selected(TreeItem *p_from) const {