[BUG] Single player can change DM to Player and loose access to DM

[10leej]

Describe the bug
TiL you can be the only player in a campaign, change yourself form DM to player and loose access to the campaign, lmao

To Reproduce
Steps to reproduce the behavior:

1. Create a campaign with only a single player.
2. Open DM Settings
3. Change your role from DM to Player
4. Find yourself with no way to get DM priviledges back.

Expected behavior
Option should be greyed out when only a single player is detected.

Additional context
The fix is to go back to the main dashboard, export the campaign, then delete the old one, and then re-upload it. Since import and export are still beta tools this can potentially cause data loss though I've encountered none in my testing of this bug.