tell coverity that ret_princ returns an allocated pointer

lib/krb5/principal.c

@@ -1178,6 +1178,7 @@ struct krb5_name_canon_rule {
  * @ingroup krb5_principal
  */
 
+/* coverity[+alloc : arg-*4] */
 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
 krb5_sname_to_principal(krb5_context context,
 			const char *hostname,
@@ -1190,6 +1191,8 @@ krb5_sname_to_principal(krb5_context context,
     register char *cp;
     char localname[MAXHOSTNAMELEN];
 
+    *ret_princ = NULL;
+
     if ((type != KRB5_NT_UNKNOWN) &&
 	(type != KRB5_NT_SRV_HST))
 	return KRB5_SNAME_UNSUPP_NAMETYPE;