Function check_header

Reads the @c Format_description_log_event from the beginning of a local input file. The @c Format_description_log_event is only read if it is outside the range specified with @c --start-position; otherwise, it will be seen later. If this is an old binlog, a fake @c Format_description_event is created. This also prints a @c Format_description_log_event to the output, unless we reach