Fix attribute Name not found

In case, a object has a Material property, and the material has no "Name"
attribute, a exception is raised when texturing it. To prevent this from
happening, we check if the material has a Name. If not, we simply ignore
the object and do not texture it.

fixes #36

texture_manager.py

@@ -198,6 +198,11 @@ def isTexturable(self, o):
 
         if not hasattr(o, 'Material') or o.Material is None:
             return False
+
+        material = o.Material
+
+        if not hasattr(material, 'Name') or material.Name is None:
+            return False
 
         return o.ViewObject.Visibility