hero location bookkeeping bit

hero location bookkeeping bit

     On the first move of the game and the first move after each level
change, the "previous position's coordinates" <u.ux0, u.uy0> had bogus
values:  zero at start, last location on old level otherwise.  They're
never used to undo a level change, so the last location on the old level
isn't interesting.  Set them to match current location, as if you'd just
rested on the new spot.  I'm not aware of any bugs attributable to this.