Fix incorrect handling of "other" headers in tfw_http_parse_resp()

- The 'p' pointer was reset to a possibly NULL value, and then used
  in a check. Do not reset the 'p' pointer. Also, the move forward
  was for a wrong number of bytes.
- Use uniform variable names and code constructs when searching for
  a LF, CR, comma, or space characters.
- Reformat several identical comments for better readability.