Improving performance of --show #2

[mohemiv]

Related: #3988

This PR adds a redundant signature check to modules 01711, 02100, 07500, 13100, 13400, 18200, 19600, 19700, 19800, 19900, 20200, 20300, 20400, 28800, 28900, and 29700 to enhance potfile reading performance.

These algorithms are the ones most commonly used in penetration testing. Enhancing them should improve the user experience.

Regarding magic constants in the code:

  /**
   * Checking the signature for performance optimization
   */

  if (line_len < 64) return (PARSER_SALT_LENGTH);

  if (strncmp(line_buf, SIGNATURE_SHA512B64S, strlen (SIGNATURE_SHA512B64S))) {
    return (PARSER_SIGNATURE_UNMATCHED);
  }

It wasn't initially introduced by me. I just increased the already existed constants:

  // assume no signature found
  if (line_len < 12) return (PARSER_SALT_LENGTH);

If you would like to change something, I'm ready to hear your suggestions.