Fixed transcode bug affecting gameplay

jotd has found and fixed a transcode bug which prevented the game from getting harder each frame.

Another transcode bug caused occasional tiles to appear randomly. This has been fixed.

Starfield has been updated. It more closely resembles the original, at least in terms of star density and colour & distribution. However there is likely a transpose error which mirrors and/or rotates the field. Blinking of stars does not attempt to emulate the original behaviour either. I've spent enough time on something that doesn't affect gameplay in any way, shape or form - I am not going to modify this any further.