Texture alpha needlessly extended

[Jacky720]

I'm using this project as a basis for a Blender importer, and I've noticed this during testing.

The texture 09d1bf.tga in rai_def_mt.tri seems to be unpacking incorrectly. The TGA dumped when exporting Raiden as an FBX looks like this:

while in my replica, I got some out of range errors regarding extend_alpha(). Removing the call to extend_alpha and instead passing the byte directly in paintPixels allowed me to instead export this:

My current guess is that the alpha modification is only necessary for PSM == 0x14 (which I haven't implemented yet), and PSM == 0x13 textures like this should use the byte directly (it's also possible I should be scaling the alpha in some other, slightly less extreme way, but I'm not sure how to ascertain that exact value except by finding the maximum alpha used in this type of texture).