add tolerance for empty choices #1563

Job	Run time
format	17s
lint	32s
docs (./packages/autogen-core)	43s
mypy (./packages/autogen-core)	1m 24s
pyright (./packages/autogen-core)	39s
mypy (./packages/autogen-magentic-one)	39s
test (./packages/autogen-core)	43s
pyright (./packages/autogen-magentic-one)	31s
mypy (./packages/agbench)	26s
test (./packages/autogen-magentic-one)	56s
pyright (./packages/agbench)	20s
test (./packages/autogen-ext)	1m 11s
mypy (./packages/autogen-ext)	53s
pyright (./packages/autogen-ext)	29s
test (./packages/autogen-agentchat)	34s
mypy (./packages/autogen-agentchat)	37s
pyright (./packages/autogen-agentchat)	23s
check-proto-changes-python	33s
	11m 50s

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