fixing a delete without checking for the existence of the object
fixing a delete without checking for the existence of the object

Summary: QMatrix deconstructor deleting "codes_" without checking its size. Check added.

Reviewed By: EdouardGrave

Differential Revision: D5227043

fbshipit-source-id: 84cfafbb039aa3a59d5b9fdaf66b3c1571460fb5

facebookresearch/fastText,facebookresearch/fastText,facebookresearch/fastText,facebookresearch/fastText,facebookresearch/fastText,facebookresearch/fastText