curl: CVE-2026-8925: SASL double-free

Hi all, We found a double-free in the GSASL authentication path — Curlauthgsaslissupported frees gsasl-ctx on a failed gsaslclientstart but never nulls the pointer, and then Curlauthgsaslcleanup frees it again unconditionally at connection teardown. The bug lives in two spots...