token: avoid undef warning if no tokens are configured

token: avoid undef warning if no tokens are configured

Initially the config may not even exist, and so the first token
create would give one then a ugly warning like:
> Use of uninitialized value $raw in split at ..

Handle that case, empty config (where we get '') was fine already, so
explicitly check for definedness, not truthiness.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>