Fixed shutting down a world with a Journal Entry Page open causing the ProseMirrorAuthority to throw an error

[Fyorl]

Originally reported by ghost#2000 https://discord.com/channels/170995199584108546/956306859491471420/998255378431234200

ALL MODULES DISABLED? true
OS, Hosting, Browser (if applicable): Arch Linux, nodejs, Chromium
Short Description of bug: Got a weird error message in the console running the nodejs app, something about prosemirror.
Simple steps to reproduce the bug: I just shut down a world, but no idea if it's reproducible reliably.
Screenshots and/or console errors:

FoundryVTT | 2022-07-17 17:48:00 | [error] Cannot read properties of undefined (reading 'find')
TypeError: Cannot read properties of undefined (reading 'find')
    at Function.#l (file:///home/johannesloher/Games/FoundryVTT-10.273/resources/app/dist/components/prosemirror.mjs:1:2765)
    at Socket.emit (node:events:532:35)
    at Socket.emit (node:domain:475:12)
    at Socket.emitReserved (/home/johannesloher/Games/FoundryVTT-10.273/resources/app/node_modules/socket.io/dist/typed-events.js:56:22)
    at Socket._onclose (/home/johannesloher/Games/FoundryVTT-10.273/resources/app/node_modules/socket.io/dist/socket.js:357:14)
    at Client.onclose (/home/johannesloher/Games/FoundryVTT-10.273/resources/app/node_modules/socket.io/dist/client.js:246:20)
    at Socket.emit (node:events:532:35)
    at Socket.emit (node:domain:475:12)
    at Socket.onClose (/home/johannesloher/Games/FoundryVTT-10.273/resources/app/node_modules/engine.io/build/socket.js:304:18)
    at Object.onceWrapper (node:events:639:28)