Function correct_field 

pub fn correct_field(input: &[u8]) -> IResult<&[u8], Kv2<'_>>

Optional field

field      =   field-name ":" unstructured CRLF
field-name =   1*ftext
ftext      =   %d33-57 /          ; Printable US-ASCII
               %d59-126           ;  characters not including
                                  ;  ":".