.Net: Fix Bug: ChatCompletionAgent without Description hangs indefinitely #28156

Job	Run time
paths-filter	7s
Python Pre-Merge Integration Tests - Agents	-1s
Python Pre-Merge Integration Tests - Multi-Modality	-1s
python-integration-tests-check	4s
Python Pre-Merge Integration Tests - AI Services (incl samples using those)	-1s
Python Integration Tests - Scheduled run	-1s
Python Pre-Merge Integration Tests - Memory (incl samples using those)	-1s
Python Pre-Merge Integration Tests - Ollama	-1s
	5s

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