server : move chat-template thinking probe inside the init try/catch (#24093)

server : move chat-template thinking probe inside the init try/catch (#24093)

A model whose chat template parses at init but fails parser generation
at apply time (e.g. uses {% call %}) throws std::invalid_argument from
common_chat_templates_support_enable_thinking(), which ran outside the
try/catch guarding common_chat_templates_init(). The throw was uncaught
and llama-cli aborted (SIGABRT) instead of failing to load. Moved the
probe inside that try/catch so an apply-time error fails load the same
way an init parse error does.

Signed-off-by: Jesse LaRose <redacted>