Correct mechanics when trying to use a 0 PP move

There are two cases where a pokemon might attempt to execute a move
with zero PP:

- a move which had PP when selected, but whose PP was subsequently
  reduced to 0 by Spite; and

- a case where a pokemon has multiple copies of the same move, in
  which case it will always be possible to select the move, but it
  will not be executed if it has 0 PP.

Attempting to use a move with zero PP should not succeed.