fix(wm): address toggle-float container edge case

This commit ensures that the focused container index on a workspace is
updated appropriately if the user calls toggle-float on the last
Container in a Ring. Previously, doing this would leave a ghost tile.
Now that we check if the focused_idx is still valid after removing an
empty Container from the workspace, users will no longer be left with a
ghost tile.

komorebi/src/workspace.rs

@@ -843,6 +843,10 @@ impl Workspace {
             if container.windows().is_empty() {
                 self.containers_mut().remove(focused_idx);
                 self.resize_dimensions_mut().remove(focused_idx);
+
+                if focused_idx == self.containers().len() {
+                    self.focus_container(focused_idx - 1);
+                }
             } else {
                 container.load_focused_window();
             }