Fix check_termination_and_human_reply() when called with empty list as messages

[davorrunje]

Why are these changes needed?

Related issue number

Closes #1124

Checks

• I've included any doc changes needed for https://docs.ag2.ai/. See https://docs.ag2.ai/docs/contributor-guide/documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
autogen/agentchat/conversable_agent.py	0.00%	1 Missing and 1 partial ⚠️

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Flag	BASE (bb8b41a)	HEAD (ff25636)
3.13	84	0
ubuntu-latest	138	1
commsagent-discord	7	0
optional-deps	137	0
browser-use	7	0
macos-latest	104	0
3.9	73	0
commsagent-slack	9	0
windows-latest	104	0
core-without-llm	9	1
3.11	62	1
3.10	92	0
commsagent-telegram	9	0
3.12	35	0
jupyter-executor	9	0
retrievechat-pgvector	10	0
graph-rag-falkor-db	6	0
retrievechat-qdrant	11	0
retrievechat-mongodb	10	0
twilio	9	0
gpt-assistant-agent	3	0
anthropic	16	0
gemini	14	0
teachable	4	0
retrievechat	10	0
lmm	4	0
websurfer	15	0
cerebras	14	0
interop	13	0
agent-eval	1	0
cohere	15	0
groq	14	0
llama-index-agent	3	0
retrievechat-couchbase	3	0
core-llm	3	0
deepseek	1	0
openai	1	0
integration	12	0
crawl4ai	13	0
falkordb	2	0
autobuild	1	0
docs	6	0
interop-crewai	9	0
interop-langchain	9	0
websockets	9	0
interop-pydantic-ai	9	0
neo4j	2	0
mistral	14	0
ollama	14	0
together	14	0
long-context	3	0
bedrock	14	0
reasoning	14	0

Files with missing lines	Coverage Δ
autogen/agentchat/conversable_agent.py	66.59% <0.00%> (-10.00%)	⬇️

... and 61 files with indirect coverage changes