CID 318094: Null pointer dereferences (REVERSE_INULL)

Remove redundant version == NULL check. This should have been included in 3b11bacb.

*** CID 318094:  Null pointer dereferences  (REVERSE_INULL)
/lib/dns/rbtdb.c: 1389 in newversion()
1383     	version->xfrsize = rbtdb->current_version->xfrsize;
1384     	RWUNLOCK(&rbtdb->current_version->rwlock, isc_rwlocktype_read);
1385     	rbtdb->next_serial++;
1386     	rbtdb->future_version = version;
1387     	RBTDB_UNLOCK(&rbtdb->lock, isc_rwlocktype_write);
1388     
   CID 318094:  Null pointer dereferences  (REVERSE_INULL)
   Null-checking "version" suggests that it may be null, but it has already been dereferenced on all paths leading to the check.
1389     	if (version == NULL) {
1390     		return (result);
1391     	}
1392     
1393     	*versionp = version;
1394