fix B15003 - behavior of bribe-able demons

fix B15003 - behavior of bribe-able demons

     Prevent a demon who is carrying the Amulet of Yendor from being
removed from the game when player meets his demand for a bribe since
that was effectively destroying the Amulet.  There are various ways
to accomplish this; I chose to make the bribe demand be for an amount
that the player cannot possibly satisfy in that case.