TreeList throws exception with dynamic setRoot

[evant]

Test Case: https://fiddle.sencha.com/#view/editor&fiddle/2lse

Run the test case, see there's an exception thrown in the console in onNodeAppend.

[evant]

Potential fix:

Ext.define(null, {
    override: 'Ext.data.TreeStore',

    updateRoot(newRoot, oldRoot) {
        this.fireEvent('beforerootchange', newRoot, newRoot, oldRoot);
        const initial = this.isConfiguring;
        // The rest of the fn
    }
});

Ext.define(null, {
    override: 'Ext.list.Tree',

    updateStore: function(store, oldStore) {
        let root;

        if (oldStore) {
            // Store could be already destroyed upstream
            if (!oldStore.destroyed) {
                if (oldStore.getAutoDestroy()) {
                    oldStore.destroy();
                } else {
                    this.storeListeners.destroy();
                }
            }
            this.removeRoot();
            this.storeListeners = null;
        }

        if (store) {
            this.storeListeners = store.on({
                destroyable: true,
                scope: this,
                filterchange: 'onFilterChange',
                nodeappend: 'onNodeAppend',
                nodecollapse: 'onNodeCollapse',
                nodeexpand: 'onNodeExpand',
                nodeinsert: 'onNodeInsert',
                noderemove: 'onNodeRemove',
                beforerootchange: 'onBeforeRootChange',
                rootchange: 'onRootChange',
                update: 'onNodeUpdate'
            });

            root = store.getRoot();
            if (root) {
                this.createRootItem(root);
            }
        }

        if (!this.destroying) {
            this.updateLayout();
        }
    },

    privates: {
        onBeforeRootChange() {
            this.rootChanging = true;
        },

        onRootChange(root) {
            this.rootChanging = false;
            this.callParent([root]);
        },

        onNodeAppend(parentNode, node) {
            if (this.rootChanging) {
                return;
            }
            this.callParent([parentNode, node]);
        }
    }
});

IMO the initial flag is incorrectly set only if we didn't have a root before. The intent is to not do those things during construction, however the root can come at a later time.