handling nlp divide by zero (#926)

* handling nlp divide by zero

* catching zerodivisionerror

* catching zerodivisionerror

* catching zerodivisionerror

* addressing comments

* addressing comments

* updating test case

* update

* add blank to last line

* update nlp notebook

* rerun

* rerun

* sync with main

* add model selection for nlg

* addressing keyerror

* add raise exception

* update

* fix bug

* revert

* updating automl_nlp

* Update flaml/automl/model.py

Co-authored-by: Zvi Baratz <z.baratz@gmail.com>

* address comments

* address comments

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Co-authored-by: Li Jiang <lijiang1@microsoft.com>
Co-authored-by: Zvi Baratz <z.baratz@gmail.com>