Fix jittery playlab movement

[balderdash]

The move actor <x> up <y> pixels blocks generate a moveDistance command that stays in the queue for however many ticks it takes to move y pixels. However, they currently stay in the queue until the first tick for which they had 0 queued distance remaining, rather than being removed in the tick on which they completed. Since no new commands are enqueued unless the current queue is empty, the sprite will stop moving for 1 tick even if you're holding down the arrow button/key the whole time.

This removes the moveDistance command from the queue as soon as the queued distance reaches zero, getting rid of the jitter.

In normal playlab this is usually masked by the ticksBeforeFaceSouth property, but it's very visible in starwars or if you hold down two arrow keys to move diagonally.

Before:

After: