Fixes merging of IDs from mal-id-cache in indexers

[irfan-dahir]

For some reason

$ids = $ids['sfw'] + $ids['nsfw']; // merge

This does not work. The NSFW array does not get included in the storage output of the next line.

Storage::put('indexer/manga_mal_id_sweep.json', json_encode($ids));

No clue why. #justPHPThings

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This works instead:

$ids = array_merge($ids['sfw'], $ids['nsfw']);