Fix CubeMap Bug

* Adds a sanity check that raises an error if a CubeMap doesn't have an image.

korman/exporter/material.py

@@ -701,6 +701,9 @@ class MaterialConverter:
             layer.texture = pl_env.key
 
     def export_cubic_env(self, bo, layer, texture):
+        if texture.image == None:
+            raise ExportError("CubeMap '{}' has no cube image!".format(texture.name))
+        else:
             width, height = texture.image.size
 
             # Sanity check: the image here should be 3x2 faces, so we should not have any
@@ -719,7 +722,7 @@ class MaterialConverter:
             # to a big "finalize" save step to prevent races. The texture cache would
             # prevent that as well, so we could theoretically slice-and-dice the single
             # image here... but... meh. Offloading taim.
-        self.export_prepared_image(texture=texture, owner=layer,
+            self.export_prepared_image(texture=texture, owner=layer, indent=3,
                                        alpha_type=TextureAlpha.opaque, mipmap=True,
                                        allowed_formats={"DDS"}, is_cube_map=True, tag="cubemap")