Null Window Entry
This item is one of the three possible items that start a GUI stack
entry: GUIR Null, GUIR Small Window, and GUIR Large Window. This item
only acts as a placeholder and container for the data within it; it does
not render anything to the screen.
Type ID: 0
Datalength: 1 byte
0: $FF (used by the rendering routines) [1 byte]