Don't generate 1x1 mip levels due to bug in Plasma

Cyan calculates the level sizes wrongly such that a 1x1 DXT5 mip level
only has one block for alpha and therefore lacks the color block. This can
cause Blender to crash with an access violation.

korman/exporter/material.py

@@ -272,6 +272,14 @@ class MaterialConverter:
             compression = plBitmap.kDirectXCompression
             dxt = plBitmap.kDXT5 if key.use_alpha or key.calc_alpha else plBitmap.kDXT1
 
+            # HACK ATTACK!
+            # There is a bug in Cyan's level size algorithm that causes it to not allocate enough memory
+            # for the color block in a 1x1 DXT5 mipmap. To fix that, we will reduce the number of levels
+            # by one, such that we don't even produce a 1x1 mipmap. DXT images need to have at least 4 pixels anyway...
+            # We can't fix the real source of the bug because the values generated by the algo are
+            # used to read from the file. Can't fixed close source games :(
+            numLevels -= 1
+
             # Grab the image data from OpenGL and stuff it into the plBitmap
             with _GLTexture(image) as glimage:
                 if key.mipmap: