fix(android): prevent NPE in WebSocketClient.sendFrame() after disconnect

[hobostay]

Summary

• Fix NullPointerException in WebSocketClient.sendFrame() that occurs when sending data after disconnect() has been called
• disconnect() sets mSocket = null on the handler thread, but sendFrame() is also posted to the same handler thread and accesses mSocket.getOutputStream() without a null check
• Added a null guard before accessing mSocket to gracefully skip the send when the socket has been closed

How the bug occurs

1. WebSocket connection is established
2. disconnect() is called, which posts a Runnable to mHandler that sets mSocket = null
3. Meanwhile, sendFrame() is also posted to mHandler (from send() or pong response)
4. If sendFrame runs after disconnect, mSocket is null → NullPointerException

Test plan

• Connect a WebSocket, send messages, then disconnect and verify no NPE
• Verify that send operations after disconnect are silently skipped (no crash)
• Verify normal WebSocket communication is unaffected

🤖 Generated with Claude Code

[hippy-service]

Hi, @hobostay. Thanks for your PR! 👏

🏷️ You can leave a comment in this PR with #help tag when you need help (e.g. some status checks run failed due to internal issue), admin team members will help asap.

[tencent-adm]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 5 committers have signed the CLA.

✅ wwwcg
✅ zealotchen0
❌ 1780243524
❌ etkmao
❌ Test User

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