Recognise "Not found" as an error and don't mark it as submitted

[Freso]

> abzsubmit .

[...       ] processing /tmp/freso-tmp
[...       ] /tmp/freso-tmp/Various Artists - Fly Girls_ B‐Boys Beware - Revenge of the Super Female Rappers_ _Disc 2 of 2_ (2009) [FLAC]/10. Roxanne Sh[:( submit ] /tmp/freso-tmp/Various Artists - Fly Girls_ B‐Boys Beware - Revenge of the Super Female Rappers_ _Disc 2 of 2_ (2009) [FLAC]/10. Roxanne Shanté - Bite This.flac
{
  "message": "Not found"
}

[:)        ] /tmp/freso-tmp/Various Artists - Fly Girls_ B‐Boys Beware - Revenge of the Super Female Rappers_ _Disc 2 of 2_ (2009) [FLAC]/10. Roxanne Shanté - Bite This.flac
[...       ] /tmp/freso-tmp/Various Artists - Fly Girls_ B‐Boys Beware - Revenge of the Super Female Rappers_ _Disc 2 of 2_ (2009) [FLAC]/09. Tina B - J[:( submit ] /tmp/freso-tmp/Various Artists - Fly Girls_ B‐Boys Beware - Revenge of the Super Female Rappers_ _Disc 2 of 2_ (2009) [FLAC]/09. Tina B - Jazzy Sensation.flac
{
  "message": "Not found"
}

[:)        ] /tmp/freso-tmp/Various Artists - Fly Girls_ B‐Boys Beware - Revenge of the Super Female Rappers_ _Disc 2 of 2_ (2009) [FLAC]/09. Tina B - Jazzy Sensation.flac
(…)

Saves to log db with reason set to NULL even though submission endpoint was "not found".

(See also https://tickets.metabrainz.org/browse/AB-368 )