Silence unchecked return of dns_db_find()

Silence unchecked return of dns_db_find()

190        dns_rdataset_init(&rdataset);
   	3. Condition r == 0, taking true branch.
   	4. Condition result, taking false branch.

	CID 1452691 (#1 of 1): Unchecked return value (CHECKED_RETURN)
	5. check_return: Calling dns_db_find without checking return
	value (as is done elsewhere 39 out of 45 times).

191        check_assertion(dns_db_find(db1, dns_rootname, v2,
192                                    dns_rdatatype_soa, 0, 0, NULL,
193                                    name, &rdataset, NULL));

(cherry picked from commit e8bf82efc6dfffa7f17117617c6dfe32ce7ac96d)