DockState<Tab>::remove_tab may cause the whole program panic when the tab is the last tab of a window.

[sakura6264]

Describe the bug
when use remove_tab function to remove the last tab from a window, it could not close the window like clicking on the tab.
And in the next time I call egui_dock::DockArea::show_inside, the program panic.

To Reproduce
Steps to reproduce the behavior:

match self.tree.find_tab(&tab) {
                        Some(index) => {
                            self.tree.remove_tab(index);
                        }
                        None => {
                            self.tree.add_window(vec![tab]);
                        }
                    }

Is there any way to close the tab from rust code just like what it happens when I click the close button?

[Adanos020]

Is there any way to close the tab from rust code just like what it happens when I click the close button?

Yes, you can override TabViewer::force_close.

[sakura6264]

This function works. Thanks very much.

[Adanos020]

Now to actually fix the issue: looks like tabs in windows aren't correctly deleted with DockState::remove_tab, leaving a Surface without a leaf node. We need to also delete the surface when that happens.