fix(editor): should not show toolbar when elements have been deleted (#11026)

Closes: [BS-2691](https://linear.app/affine-design/issue/BS-2691/[bug]-当-edgeless-为空的时候，点击-space-会在左上角出现一个莫名的-toolbar)

blocksuite/affine/widgets/widget-toolbar/src/toolbar.ts

@@ -157,6 +157,9 @@ export class AffineToolbarWidget extends WidgetComponent {
         .map(id => gfx.getElementById(id))
         .filter(model => model !== null) as GfxModel[];
 
+      // Should double check
+      activated &&= Boolean(elements.length);
+
       hasLocked = elements.some(e => e.isLocked());
 
       const grouped = groupBy(