[Bugfix] Only print out chat template when supplied

[terrytangyuan]

Currently None is printed out. We should only print it when the chat template is supplied.

INFO 02-18 01:35:41 executor_base.py:115] Maximum concurrency for 32768 tokens per request: 1.00x
INFO 02-18 01:35:43 llm_engine.py:431] init engine (profile, create kv cache, warmup model) took 1.15 seconds
INFO 02-18 01:35:43 api_server.py:756] Using supplied chat template:
INFO 02-18 01:35:43 api_server.py:756] None

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[jeejeelee]

Thank you for this improvement