Function module_to_talkgroup 

fn module_to_talkgroup(module: Option<&str>) -> String

Returns the Rdio Scanner talkgroup id for a D-STAR module letter.

A → 1, B → 2, …, Z → 26. Any other input (including None, empty strings, lowercase letters, multi-byte strings) falls back to "0" so the upload still goes through with a sentinel value the server can filter on.