Close #148.

This isn't the best fix in the world. We don't really know what the user
did to cause the failure because of how abstract this code is. A proper
fix would be to ensure region modifiers can't get attached to non-mesh
objects. That won't fix already "broken" stuff in blend files without
being naughty/destructive, however.

korman/exporter/physics.py

@@ -43,7 +43,11 @@ class PhysicsConverter:
         return indices
 
     def _convert_mesh_data(self, bo, physical, indices=True, mesh_func=None):
-        mesh = bo.to_mesh(bpy.context.scene, True, "RENDER", calc_tessface=False)
+        try:
+            mesh = bo.to_mesh(bpy.context.scene, True, "RENDER", calc_tessface=False)
+        except:
+            raise ExportError("Unable to convert object [{}] '{}' to a mesh. Make sure you didn't try to use this object as a region!",
+                              bo.type, bo.name)
         mat = bo.matrix_world
 
         with TemporaryObject(mesh, bpy.data.meshes.remove):