Fix skill selection menu repainting

[lethal-guitar]

The skill description string at the bottom (e.g. "less enemies, more powerups") is not repainted correctly when switching between skills. This is because the script for the skill selection uses a mixture of big and regular text in a single XYTEXT command. The spaces preceding the big-text marker are supposed to paint over the previously shown skill description message.

To fix, XYTEXT should result in both a DrawText and a DrawBigText action when there are characters preceding the big-text marker byte.