tls13: set sess_free_cb to null after calling.

[philljj]

Description

Set ->sess_free_cb = NULL; after calling session free callback and nulling the session.

Fixes zd#22190.

[Copilot]

Pull request overview

This PR hardens the TLS 1.3 PSK/session-ticket handling in DoPreSharedKeys() by clearing the session free callback pointer after it has been invoked, alongside the existing session pointer and callback-context cleanup. This reduces the chance of accidental double-invocation if the current PSK entry is revisited or reused after cleanup.

Changes:

• After invoking current->sess_free_cb(...), set current->sess_free_cb = NULL in all relevant cleanup paths.
• Keep cleanup consistent with the existing pattern of nulling current->sess and zeroing current->sess_free_cb_ctx.

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[github-actions]

MemBrowse Memory Report

gcc-arm-cortex-m4-openssl-compat

• FLASH: .text +64 B (+0.0%, 769,724 B / 1,048,576 B, total: 73% used)
  No memory changes detected for:
• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m3
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-pq
• gcc-arm-cortex-m4-rsa-only
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m4-tls13
• gcc-arm-cortex-m7
• gcc-arm-cortex-m7-pq
• gcc-arm-cortex-m7-tls13
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753