fix compiler crash

Cython/Compiler/Nodes.py

@@ -1199,6 +1199,7 @@ class CppClassNode(CStructOrUnionDefNode, BlockNode):
         if self.entry is None:
             return
         self.entry.is_cpp_class = 1
+        if scope is not None:
             scope.type = self.entry.type
         defined_funcs = []
         if self.attributes is not None: