amulets may be made from various materials
Feeling of draining energy is now correct

Feeling of amulet draining energy away is now correct in all situations

Fixes "You feel the amulet draining your energy away. You don't have
enough energy to cast that spell." that caused no energy change.

Awkward double check of energy > u.uen is to protect from amulet
draining power from spell that anyway is unable to succeed.
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