fix #H5856 - Amulet draining energy

fix #H5856 - Amulet draining energy

The sequence
  You feel the amulet draining your energy away.
  You don't have enough energy to cast that spell.
didn't use any energy or cost any time so the player could try over
and over until the randomly chosen drain amount happened to be low
enough to succeed.

The old behavior was that the cost of the current cast attempt got
incresed by a random amount.  Now, if hero already lacks sufficient
energy to cast the spell, the Amulet's effect won't take place, the
second message will be given, and no energy or time will be consumed.
When there is enough energy to cast the spell, the drain effect will
occur and some energy will be used up immediately (instead of
increasing the cost of this attempt).  The energy drain might then
result in the second message, but if so, a turn will be used.

No longer increasing the energy cost of the current cast has a
side-effect on not increasing the hunger penalty for the current cast
(since that is based on the energy cost) but the energy drain message
doesn't actually imply any effect on hunger.