alliance_roles_processing.php: fix phpstan warning
alliance_roles_processing.php: fix phpstan warning

> Variable $role_id might not be defined.

The result will never be null because alliances are auto-bestowed some
roles on creation.

hemberger/smr,hemberger/smr,smrealms/smr,smrealms/smr,smrealms/smr,hemberger/smr,hemberger/smr