If the crack doesn't disappear while you are shaping the grip, lay a good app of CA (cyanoacrylate glue) to the crack. Thin or extra thin glue will wick up into the crack and seal it, preventing further splitting.
I built an English warbow a few years ago from a billet of yew wood and after I removed the bark from the log, I found a number of drying checks running lengthwise. I simply laid on apps of CA until the cracks were filled, and the bow has never suffered from the effect of being cracked. It draws 100 pounds at 32".