Unclear when this can happen currently (hence missing a test), but this adds a safeguard to `applyUrlFromHistoryPushReplace` to ensure that we don't potentially call `ACTION_RESTORE` with data that might be missing from `window.history.state`.
This is consistent with other spots where we're reading this internal flag from state.
The function that calls `applyUrlFromHistoryPushReplace` first calls `copyNextJsInternalHistoryState` to copy over `__PRIVATE_NEXTJS_INTERNALS_TREE` into the data argument of `pushState`/`replaceState`. But technically it does so with the possibility that `__PRIVATE_NEXTJS_INTERNALS_TREE` is undefined. Since that's the case, this is more typesafe.
Closes NEXT-2406
6f74618486