o Minor bugfixes
    - Stop failing when key files are zero-length. Instead, generate new
      keys, and overwrite the empty key files.
      Fixes bug 13111.
    - Stop generating a fresh .old RSA key file when the .old file is missing.
      Fixed as part of bug 13111.
    - Avoid overwriting .old key files with empty key files.
      Fixed as part of bug 13111.
    - Stop crashing when a NULL filename is passed to file_status().
      Fixed as part of bug 13111.

  o Minor enhancements:
    - Skip loading zero-length extra info store, router store, stats, state,
      and key files.
      Implemented with bug 13111.
    - Return FN_ERROR when a zero-length filename is passed to file_status().
      Fixed as part of bug 13111.