Walking anim offsets need fine-tuning

[rozniak]

Now that the walking code appears to be 1-to-1 with the original game, it looks like additional work is required on the walking animation itself. Most noticable when Junkbot is walking down stairs to the left, his sprite displays a Z ordering problem... I think this is simply down to the position of his sprite rather than a rendering problem.

Going to have to go frame-by-frame on the original to see how they compare in order to correct them.