Cantrips that require concentration should not warn that you have no available spell slots

[bentomhall]

Steps

1. Create a cantrip that requires concentration. Or use the SRD version of guidance.
2. Add it to a spell-caster.
3. Click on the spell to cast it.

Expected
I get the spell popup, but no warnings about spell slots.

Actual
I get big warnings about not having the required spell slot...for a cantrip.

Warnings:

[bemdesign-er]

Additional info:

• This also occurs when a cantrip has an area of effect - e.g. setting the Target to 5 feet cube on a cantrip will also cause this "You have no available spell slots with which to cast ".
  It appears to happen if there is anything to pick.