[BUG] importing artwork choices fails if game was uninstalled

[wec22]

• Describe the bug
  If a game that was previously parsed when the artwork choices were exported is removed, attempting to import those artwork choices fails. You can edit the _selections.json to remove the entry for the missing game and it will import correctly again.

• Steps to reproduce the behavior

1. export artwork choices
2. remove game from system
3. rescan library
4. attempt to import artwork choices

• Expected behavior
  Import parser should import the entries it can and ignore entries in _selections.json that aren't found. Could provide a warning or message for transparency.

• Screenshots
  

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[Drahsid]

I was investigating this because a friend of mine ran into this issue and we were able to bypass this error by modifying isLocalImageUnique in src/renderer/services/preview.service.ts:

isLocalImageUnique(
  imageKey: string,
  imageUrl: string,
  artworkType: ArtworkType,
  provider: MultiLocalProviderType,
) {
    if (this.onlineImages[artworkType][imageKey]?.offline === undefined || this.onlineImages[artworkType][imageKey]?.offline?.[provider] === undefined) {
      return false;
    }
    else {
      return (this.onlineImages[artworkType][imageKey].offline[provider].findIndex(
        (item) => item.imageUrl === imageUrl,
      ) === -1);
    }
}

This isn't particularly ideal, it would probably be better to create a list of missing titles and report them to the user as some sort of warning. The existing error is pretty unclear, and pretty impossible to identify for the layman.