Added NULL check to rrset_deep_free.

src/dnslib/rrset.c

@@ -119,7 +119,7 @@ void dnslib_rrset_deep_free(dnslib_rrset_t **rrset, int free_owner,
 	dnslib_rdata_t *next_rdata;
 	tmp_rdata = (*rrset)->rdata;
 
-	while ((tmp_rdata->next != (*rrset)->rdata) &&
+	while ((tmp_rdata != NULL) && (tmp_rdata->next != (*rrset)->rdata) &&
 		(tmp_rdata->next != NULL)) {
 		next_rdata = tmp_rdata->next;
 		dnslib_rdata_deep_free(&tmp_rdata, (*rrset)->type,