Parallel Intercepted routes not working when accessed from 404 error pages

### Link to the code that reproduces this issue https://github.com/itsjavi/nextjs-demos/tree/issue/parallel-intercepted-404 ### To Reproduce 1. Add a parallel intercepted route [like in this example](https://github.com/itsjavi/nextjs-demos/tree/issue/parallel-intercepted-404/src/app) 3. Add the following to your app: - error.tsx page - support for the `@modal` slot in your layout.tsx props, and put it inside the body. - a Link in your layout.tsx, linking to the intercepted route 7. Navigate to any non-existing route to trigger a 404 error page 8. Click to the link of the layout that would trigger the intercepted route ### Current vs. Expected behavior ### Current behavior #### On `next dev` When accessing Parallel Intercepted routes from a 404 page, it triggers the following client-side error: ``` UI: Application error: a client-side exception has occurred (see the browser console for more information). Console: app-router.ts:52 TypeError: initialTree is not iterable at applyPatch (apply-router-state-patch-to-tree.ts:17:51) at applyRouterStatePatchToTree (apply-router-state-patch-to-tree.ts:107:26) at navigate-reducer.ts:208:50 The above error occurred in the <Router> component. It was handled by the <ErrorBoundaryHandler> error boundary. ``` #### On `next start` On `next start`, after build, navigating to the intercepted route from a 404 page works, but calling router.back() will trigger the same error again. ### Expected behavior - The intercepted route content is shown on 404 pages, when navigating to that route. - router.back() works as expected in all the above scenarios. ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.1.0: Thu Oct 10 21:03:15 PDT 2024; root:xnu-11215.41.3~2/RELEASE_ARM64_T6000 Available memory (MB): 32768 Available CPU cores: 10 Binaries: Node: 20.18.0 npm: 10.8.2 Yarn: 1.22.22 pnpm: 9.12.2 Relevant Packages: next: 15.0.3 // La…