closes https://github.com/assimp/assimp/issues/2439: add null ptr test before calling hasAttr.

port/PyAssimp/pyassimp/helper.py

@@ -274,6 +274,8 @@ def hasattr_silent(object, name):
     """
 
     try:
+	    if not object:
+		    return False
         return hasattr(object, name)
     except AttributeError:
         return False