reinstate warp aligned factors for BPR
reinstate warp aligned factors for BPR

This commit: https://github.com/benfred/implicit/commit/bf905636de28cf05d95c7c891b94677bd5f0647e
accidentally removed the check added in
https://github.com/benfred/implicit/commit/be25233a57c58acffa2cfd55f517c7ffb341664c . Reinstate.

benfred/implicit,benfred/implicit,benfred/implicit