add_modtime_and_size_if_missing

Fills in modification_time and size of info from info.full_name when the time is still APOLLO_TIME_INVALID. Returns whether the details are known: false, with had_error set, when they cannot be read. A record that already has a time is left alone and the answer is !had_error. visit_files fills these in itself on this target.

add_modtime_and_size_if_missing :: (info: *File_Visit_Info) -> bool