security/krb5-12?: Fix reachable assert when importing krb5 names

If a name token contains trailing garbage, error out from
krb5_gss_import_name() instead of crashing the process with an
assertion failure.

Commit message details obtained from upstream commit.
Obtained from: upstream commit 07818f1fd
Reported by: Aisle Research (Ze Sheng, Dmitrijs Trizna,

		Luigino Camastra, Guido Vranken) to krb5-bugs

MFH: 2026Q2