`Cannot read properties of null (reading 'name')` in `RoomPreviewBar.tsx`

### Steps to reproduce

See rageshake https://github.com/matrix-org/element-web-rageshakes/issues/20064

It is possible to get to line 491:

```
title = _t("Do you want to chat with %(user)s?", { user: inviteMember.name });
```

when `inviteMember` is null.

We should prevent this.

### Outcome

.

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

_No response_

### Application version

1.11.22

### Homeserver

_No response_

### Will you send logs?

Yes

Start in RoomPreviewBar.tsx at line 491, where the issue reports that inviteMember can be null while its name is read. Use the linked rageshake reproduction to trace that state and verify that reaching this path no longer causes the null-property error.

Written by the indexing model from the issue text.