fix: include assets when importing document (package tldraw) (#950)

* fix: include asset when importing document

* defensive tweak

* fixey back

Co-authored-by: Steve Ruiz <steveruizok@gmail.com>

packages/tldraw/src/state/TldrawApp.ts

@@ -1306,7 +1306,13 @@ export class TldrawApp extends StateManager<TDSnapshot> {
   updateDocument = (document: TDDocument, reason = 'updated_document'): this => {
     const prevState = this.state
 
-    const nextState = { ...prevState, document: { ...prevState.document } }
+    const nextState = {
+      ...prevState,
+      document: {
+        ...prevState.document,
+        assets: document.assets,
+      },
+    }
 
     if (!document.pages[this.currentPageId]) {
       nextState.appState = {