- extended FTexture::GetPixels and FTexture::GetColumn by a RenderStyle parameter.

Now it is no longer necessary to provide specially set up textures for rendering shaded decals, they can use any PNG texture now that contains a proper red channel.
Handling of the alPh chunk has been removed as a result as it in no longer needed.

src/gl/textures/gl_texture.cpp

@@ -238,7 +238,7 @@ void FTexture::CreateDefaultBrightmap()
 			) 
 		{
 			// May have one - let's check when we use this texture
-			const uint8_t *texbuf = GetPixels();
+			const uint8_t *texbuf = GetPixels(DefaultRenderStyle());
 			const int white = ColorMatcher.Pick(255,255,255);
 
 			int size = GetWidth() * GetHeight();