check if sha256_pak exists otherwise skip fw

[gtalusan]

This will naively skip a firmware if sha256_pak doesn't exist. There are some NVS8 firmware in the firmwares_live.json that don't have a sha256_pak in the object.

Addresses the issue that I reported at #45, and someone else at #48.

I've also added zstandard to requirements.txt.

% cat firmwares_live.json | jq '.[] | select(has("sha256_pak") | not)'
{
  "version": "v3.3.0.282_23103154",
  "filename": "NVS16_282_23103154",
  "updated_at": "2024-02-19 16:09:08+08:00",
  "note": "Recommendation for upgrade: Because there are many updates in this version, it is recommended to check the Reset Configuration option when upgrading.",
  "firmware_id": 487,
  "model": "NVS16",
  "hw_ver": "N6MB01",
  "changelog": [
    "1. Optimize the interface and interaction.",
    "2. Support setting up Night Mode Focus Enhancement for the camera RLC-823A-16X.",
    "3. Support setting up Bining Mode for 12MP cameras (only for cetain models).",
    "4. Support setting up spolight mode and HDR for cameras like CX410.",
    "5. Support Time Lapse.",
    "6. Support setting up Interframe Space and Bitrate Mode for cameras.",
    "7. Optimize the thumbnail pictures of Horizontal Tracking Range.",
    "8. Optimize TrackMix series and the model RLC-81MA when working with the NVR.",
    "9. Support upgrading firmware via the Reolink Client for those cameras added to the NVR.",
    "10.Support importing HTTPS certicate for the NVR via the Reolink Client.",
    "11. Update web client.",
    "12. Solved other known bugs."
  ],
  "display_time": "2024-02-19 00:00:00+08:00",
  "file": "https://home-cdn.reolink.us/wp-content/uploads/2024/02/190805511708329951.4053.zip",
  "error": "No PAKs found in ZIP file",
  "source": "live"
}
{
  "version": "v3.3.0.282_23103129",
  "filename": "NVS8_282_23103129",
  "updated_at": "2024-02-19 15:59:00+08:00",
  "note": "Recommendation for upgrade: Because there are many updates in this version, it is recommended to check the Reset Configuration option when upgrading.",
  "firmware_id": 486,
  "model": "NVS8",
  "hw_ver": "N7MB01",
  "changelog": [
    "1. Optimize the interface and interaction.",
    "2. Support setting up Night Mode Focus Enhancement for the camera RLC-823A-16X.",
    "3. Support setting up Bining Mode for 12MP cameras (only for cetain models).",
    "4. Support setting up spolight mode and HDR for cameras like CX410.",
    "5. Support Time Lapse.",
    "6. Support setting up Interframe Space and Bitrate Mode for cameras.",
    "7. Optimize the thumbnail pictures of Horizontal Tracking Range.",
    "8. Optimize TrackMix series and the model RLC-81MA when working with the NVR.",
    "9. Support upgrading firmware via the Reolink Client for those cameras added to the NVR.",
    "10.Support importing HTTPS certicate for the NVR via the Reolink Client.",
    "11. Update web client.",
    "12. Solved other known bugs."
  ],
  "display_time": "2024-02-19 00:00:00+08:00",
  "file": "https://home-cdn.reolink.us/wp-content/uploads/2024/02/190756371708329397.3966.zip",
  "error": "No PAKs found in ZIP file",
  "source": "live"
}