Backport a small fix from 1.12 (#1035203).

--- src/lib/krb5/krb/preauth2.c
+++ src/lib/krb5/krb/preauth2.c
@@ -1002,6 +1002,7 @@ krb5_do_preauth(krb5_context context, kr
     krb5_init_preauth_context(context);
     if (context->preauth_context == NULL) {
         *out_padata = out_pa_list;
+        out_pa_list = NULL;
         goto error;
     }