Clicking on "Add AI Player" -> "Continue" allows starting game without a player

### Description

This is confusing, should not let player start a game without them having joined it first.

### To Reproduce

1. Go to player select
2. Click "Add AI Player'
3. Click "Continue"

### Expected Behavior

Cannot start game without a player ready.

### Additional Context

_No response_

### Log Messages

_No response_