Fix textcat.begin_training if vectors set
Fix textcat.begin_training if vectors set

explosion/spaCy,spacy-io/spaCy,spacy-io/spaCy,spacy-io/spaCy,spacy-io/spaCy,explosion/spaCy,explosion/spaCy,honnibal/spaCy,explosion/spaCy,explosion/spaCy,explosion/spaCy,honnibal/spaCy,spacy-io/spaCy,spacy-io/spaCy,honnibal/spaCy,honnibal/spaCy