Fix memory leak when adding empty morph (#6581)
Fix memory leak when adding empty morph (#6581)

Fix lookup of empty morph in the morphology table, which fixes a memory
leak where a new morphology tag was allocated each time the empty morph
tag was added.
spacy-io/spaCy,spacy-io/spaCy,explosion/spaCy,explosion/spaCy,spacy-io/spaCy,spacy-io/spaCy,explosion/spaCy,spacy-io/spaCy,spacy-io/spaCy,honnibal/spaCy,honnibal/spaCy,explosion/spaCy,honnibal/spaCy,explosion/spaCy,honnibal/spaCy,explosion/spaCy