Bugfix: Clear out stratum share work before freeing it

cgminer.c

@@ -4314,6 +4314,7 @@ static void clear_stratum_shares(struct pool *pool)
 	HASH_ITER(hh, stratum_shares, sshare, tmpshare) {
 		if (sshare->work.pool == pool) {
 			HASH_DEL(stratum_shares, sshare);
+			clear_work(&sshare->work);
 			free(sshare);
 			cleared++;
 		}