Room previews as a guest are broken for some rooms

[Half-Shot]

CC: @Cadair

Reproduction steps:

• Use a fresh browser session / do not be logged in.
• Go to https://app.element.io/#/room/#matrix:matrix.org
  • Notice it previews successfully
• Go to https://app.element.io/#/room/#sunpy:openastronomy.org
  • Notice how the preview spinner spins forever

Both rooms appear to initialSync correctly, so I'm fairly certain that Element is getting the required data to show a preview and it's blowing up somewhere in the stack.

Extra context:

• The room used to have widgets, but not anymore. Some lingering state may be causing issues.

Some logs:

 error-codes.js:44:4
Stopped peeking in room !OGEhHVWSdvArJzumhm:matrix.org error-codes.js:44:4
Uncaught (in promise) TypeError: e is null
    loadRoomWidgets strings.ts:40
    p GroupAddressPicker.js:78
    emit events.js:157
    _handleEvent scheduler.js:204
    n scheduler.js:211
    emit events.js:152
    setStateEvents room-state.js:131
    d utils.ts:138
    setStateEvents room-state.js:763
    peek sync.js:132
    promise callback*m.prototype.peek sync.js:109
    peekInRoom client.js:3825
    setupRoom RoomView.tsx:1095
    X ReplaceTransition.js:38
    UNSAFE_componentWillMount RoomView.tsx:206
    React 7
    unstable_runWithPriority scheduler.production.min.js:13
    React 6
    viewRoom MatrixChat.tsx:437
    promise callback*viewRoom MatrixChat.tsx:413
    ge MatrixChat.tsx:234
    _invokeCallback setImmediate.js:126
    dispatch setImmediate.js:87
    setTimeout handler*dispatch MatrixClientPeg.ts:185
    viewRoom RoomViewStore.tsx:81
    __onDispatch Analytics.js:296
    __invokeOnDispatch FluxStoreGroup.js:15
    _dispatchToken StyledMenuItemRadio.tsx:31
    _invokeCallback setImmediate.js:126
    dispatch setImmediate.js:87
    setTimeout handler*dispatch MatrixClientPeg.ts:185
    showScreen MatrixChat.tsx:1542
    b app.tsx:61
    b app.tsx:69
    U app.tsx:146
    ne init.tsx:149
    27 index.ts:200

(I couldn't attach debug logs, as the debug logger depends on a working database)

[turt2live]

Duplicate of #8933

[Cadair]

Disagree this is a dupe, this isn't widgets aren't working this is breaking the whole room preview.

[Half-Shot]

I'm not sure this is the same. @ara4n describes widgets being unusable in rooms as a guest, whereas this is room previews being broken in a room before the user has even joined.

Also, the room doesn't have any widgets in it according to @Cadair, so let's not close issues in a rush :)

[turt2live]

Please submit logs and get a stacktrace from a develop client then - we've fixed a few bugs in the area, and one of them is probably related.

[turt2live]

(this was closed because the stacktrace provided uses widgets, and as far as the client and server are concerned you are a guest when you are previewing)

[Half-Shot]

Hmm, logs weren't terribly enlightening.

[turt2live]

The logs were also not from a develop client.

[Half-Shot]

I don't think that helped you much.

[Cadair]

Also it should be noted there are no active widgets in that room, just the remnants of them in room state.

[Cadair]

(this was closed because the stacktrace provided uses widgets, and as far as the client and server are concerned you are a guest when you are previewing)

I get this but previewing rooms used to work when there were widgets in there, even if you couldn't interact with the widgets themselves.

[turt2live]

The logs not working is #15379. As for this issue, duplicate of #15349

[Cadair]

Thanks for the triage @turt2live 😄