Fixed type error xml import of empty elements

[drfho]

An XML import into a non-schema-identical target client may result in a type error due to function xmllib.xmlOnUnknownEndTag(): in these cases value may occurs as empty list instead of dict.
This should be covered:

[zmsdev]

Can you also provide a sample xml.
We could write a unit-test for the error.

[zmsdev]

I left some comments

[drfho]

@zmsdev
Thanks for reply. I am sorry, cannot reprduce it. The once observed case revealed a type problem ([] vs {}) for unknown reasons. Because of model mismatch, the import does not work anyway. So its good enough, not to block further import. Variable lang does not seem to be relevant for causing the error.

[drfho]

@zmsdev : now the lang var is added to error info and the code covers another type error None.pop() in case of incomplete content models . Looking forward to your comments.