(core) DuplicatePage function didn't duplicated collapsed widgets

Summary:
When one of 2 widget was collapsed, the resulting widget can become a root section. Then,
when a page was duplicated, the layout was duplicated incorrectly (with wrong collapsed
section). This resulted in a bug, when the root section was deleted, as it was the last
section in the saved layout, but not the last section on the visible layout.

Test Plan: Added 2 tests

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D4227

app/client/components/ViewLayout.ts

@@ -334,7 +334,12 @@ export class ViewLayout extends DisposableWithEvents implements IDomComponent {
 
     function addToSpec(leafId: number) {
       const newBox = tmpLayout.buildLayoutBox({ leaf: leafId });
-      const rows = tmpLayout.rootBox()!.childBoxes.peek();
+      const root = tmpLayout.rootBox();
+      if (!root || root.isDisposed()) {
+        tmpLayout.setRoot(newBox);
+        return newBox;
+      }
+      const rows = root.childBoxes.peek();
       const lastRow = rows[rows.length - 1];
       if (rows.length >= 1 && lastRow.isLeaf()) {
         // Add a new child to the last row.

app/client/components/duplicatePage.ts

@@ -199,13 +199,20 @@ function newViewSectionAction(widget: IPageWidget, viewId: number) {
 /**
  * Replaces each `leaf` id in layoutSpec by its corresponding id in mapIds. Leave unchanged if id is
  * missing from mapIds.
+ * LayoutSpec is a tree structure with leaves (that have `leaf` property) or containers of leaves. The root
+ * container (or leaf) also includes a list of collapsed leaves in `collapsed` property.
+ *
+ * Example use:
+ *   patchLayoutSpec({
+ *     leaf: 1,
+*      collapsed: [{leaf: 2}]
+ *   }, {1: 10, 2: 20})
  */
 export function patchLayoutSpec(layoutSpec: any, mapIds: {[id: number]: number}) {
-  return cloneDeepWith(layoutSpec, (val) => {
-    if (typeof val === 'object' && val !== null) {
-      if (mapIds[val.leaf]) {
-        return {...val, leaf: mapIds[val.leaf]};
-      }
+  const cloned = cloneDeepWith(layoutSpec, (val, key) => {
+    if (key === 'leaf' && mapIds[val]) {
+      return mapIds[val];
     }
   });
+  return cloned;
 }