fix(core): split view solo view crash (#9432)

packages/frontend/core/src/modules/workbench/entities/workbench.ts

@@ -43,8 +43,10 @@ export class Workbench extends Entity {
   activeView$ = LiveData.computed(get => {
     const activeIndex = get(this.activeViewIndex$);
     const views = get(this.views$);
-    return views[activeIndex]; // todo: this could be null
+    // activeIndex could be out of bounds when reordering views
+    return views.at(activeIndex) || views[0];
   });
+
   location$ = LiveData.computed(get => {
     return get(get(this.activeView$).location$);
   });