This fixes https://github.com/kichikuou/xsystem35-sdl2/issues/45.
The behavior when the contents of link table differ between ALD volumes
is different between System 3.8 and System 3.9, and System 3.9 uses the
link table of the first volume. The MangaGamer version of Rance 5D
depends on this behavior.
As far as I know, the only game that depends on the System 3.8 behavior
is Child Assassin (in Alice CD 2.50). Considering the additional
complexity, we do not implement switching to the old behavior.
System3.x uses the following bit expansion when converting RGB565 to
RGB888:
RRRRR GGGGGG BBBBB => RRRRRRRR GGGGGGGG BBBBBBBB
12345 123456 12345 12345123 12345612 12345123
However, SDL's blit functions use a slightly different mapping, so
sometimes expanded color did not match the color key specified in the CX
command.
To avoid this, convert to RGB888 by ourselves when drawing 16-bit CGs.
kichikuou