fix: avoid an extra query on empty spelling suggestions
fix: avoid an extra query on empty spelling suggestions

None was being used as a placeholder to test whether to run
a spelling suggestion query but was also a possible response
when the backend didn’t return a suggestion, which meant 
that calling `spelling_suggestion()` could run a duplicate
query.
sgaist/django-haystack,antonyr/django-haystack,celerityweb/django-haystack,celerityweb/django-haystack,elishowk/django-haystack,antonyr/django-haystack,elishowk/django-haystack,sgaist/django-haystack,celerityweb/django-haystack,elishowk/django-haystack,antonyr/django-haystack,barseghyanartur/django-haystack,barseghyanartur/django-haystack,barseghyanartur/django-haystack,sgaist/django-haystack