fp2: add nil check in eventsource

[hdlee27]

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Type of Change

• WWST Certification Request
  • If this is your first time contributing code:
    • I have reviewed the README.md file
    • I have reviewed the CODE_OF_CONDUCT.md file
    • I have signed the CLA
  • I plan on entering a WWST Certification Request or have entered a request through the WWST Certification console at developer.smartthings.com
• Bug fix
• New feature
• Refactor

Checklist

• I have performed a self-review of my code
• I have commented my code in hard-to-understand areas
• I have verified my changes by testing with a device or have communicated a plan for testing
• I am adding new behavior, such as adding a sub-driver, and have added and run new unit tests to cover the new behavior

Description of Change

add nil check for sock.
As shown below, there was a driver restart due to sock nil, so there was a request for modification.

2024-11-14_05:01:00.094 | E | edi | <Aqara Presence Sensor (01976eca)> runtime error: [string "cosock.lua"]:313: [string "lunchbox/sse/eventsource.lua"]:346: attempt to index a nil value (field '_sock')

Summary of Completed Tests

complete fp2 registration test on V3

[github-actions]

Channel deleted.

[github-actions]

Test Results

   64 files    401 suites   0s ⏱️
1 999 tests 1 999 ✅ 0 💤 0 ❌
3 439 runs  3 439 ✅ 0 💤 0 ❌

Results for commit 57f68c2.

[github-actions]

Minimum allowed coverage is 90%

Generated by 🐒 cobertura-action against 57f68c2