It should not be possible to start a call in an "empty" DM?

### Steps to reproduce

1. Where are you starting? What can you see?

- Create a DM between Alice and Carl
- Let Carl leave the DM
- Try to start a call from alice

### Outcome

#### What did you expect?

That the call button is disabled? there is no one in the room

#### What happened instead?

### Operating system

macos

### Browser information

_No response_

### URL for webapp

develop

### Application version

_No response_

### Homeserver

_No response_

### Will you send logs?

No