Add a NULL check to refineSuites.

[kareem-wolfssl]

Thanks to xiaoshuai for the report.

Description

Fixes zd#21987

Testing

Built in tests

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[Copilot]

Pull request overview

This PR aims to harden refineSuites() against NULL inputs to prevent crashes when refining cipher suite lists during TLS/DTLS negotiation (Fixes zd#21987).

Changes:

• Add an early NULL check in refineSuites() for sslSuites / peerSuites.
• Set outSuites->suiteSz = 0 on early exit (when outSuites is non-NULL).

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[github-actions]

MemBrowse Memory Report

gcc-arm-cortex-m4-tls13

• FLASH: .text +64 B (+0.0%, 234,754 B / 262,144 B, total: 90% 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-openssl-compat
• 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-m7
• gcc-arm-cortex-m7-pq
• gcc-arm-cortex-m7-tls13
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753