Maps set next are ignored when pools disabled

[calcastor]

While #966 fixed an issue with set next maps being set twice, the change makes it impossible to cycle to a set next map or force-cycle to a specific map when pools are disabled.

How to replicate:

1. Configure a server with PGM, but disable pools in the PGM config
2. Ingame, use /sn to set a map, or use /cycle to cycle to a specific map. When cycling, a random map will be loaded.

If you have access to /server mapdev on OCC, this can be observed there as its PGM build has this commit, and pools are disabled in its config.

[alexsosnovsky]

I'll get on this.

[calcastor]

Closed with #979