Verify correctness of action6 offsets
The offsets computed for use with action6 are currently not checked for correctness, which can lead to subtle, nasty bugs.
I think it'd be best to verify, that the offset just past the end of the last number is equal to the sprite size.
i.e. the following three things should be equal:
- actual printed bytes
- computed sprite size
- final action6 offset
Currently, only the first two are checked.