Iterate through dict copy since the size of original is changed durin…

…g iteration

ait/core/util.py

@@ -157,7 +157,7 @@ def create(*args, **kwargs):
 
     extensions = ait.config.get('extensions', None)
 
-    for clsname, cls in modsyms.items():
+    for clsname, cls in modsyms.copy().items():
         if not isinstance(cls, type):
             continue