Fixed the problem with the class being set to 'NoneType' when using custom_calling_convention. (#382)

Author: CookStar

addons/source-python/packages/source-python/memory/manager.py

@@ -204,6 +204,7 @@ class MyCustomCallingConvention(CallingConvention):
                 MyCustomCallingConvention)
         """
         self.register_convention(cls.__name__, cls)
+        return cls
 
     def register_convention(self, name, convention):
         """Register a custom calling convention.