Some slash-commands like /myroomnick not working in „pre-DM“

### Steps to reproduce

1. Start a DM with someone, **do not** send the first message
2. Run a slash-command like `/myroomnick`

Other commands are also affected.

### Outcome

#### What did you expect?

Some commands could be executed on room creation. For instance `/myroomnick` totally makes sense.

Others should not be available. Example for that would be `/addwidget`.

#### What happened instead?

Server error - unknown room

### Operating system

Ubuntu 22.04.1 LTS

### Browser information

Firefox 103.0.2

### URL for webapp

https://develop.element.io/

### Application version

Element version: 39eee10c576f-react-0dffc582e7e5-js-3f6f5b69c7a1 Olm version: 3.2.12

### Homeserver

matrix.org

### Will you send logs?

No