[BUG] Lighting seems to be broken in some cases depending on the mesh's texture's settings

[ttbd]

This is from using models taken from official Len'en games, which use the same lighting feature; depending on the mesh's texture's settings, sometimes the lighting doesn't work at all or doesn't work correctly despite the preview in Metasequoia showing it correctly. It's a bit hard to explain, but the issues I found include:

• Setting the "value" HSV setting to anything around 70 causes the lighting to not transition smoothly between its lightest and darkest.
• Setting "diffuse" to 0 stops the lighting from working entirely.