Some pixiv sketch links can't be added or block the editing of a post's tags

[nonamethanks]

Latest example:
https://img-sketch.pixiv.net/uploads/medium/file/853888/3270289746156961930.png
I had to remove it from https://danbooru.donmai.us/posts/2428340 to edit its tags, but now I can't add it again.

The error is the following:

ActiveModel::RangeError exception raised
3270289746156961930 is out of range for ActiveModel::Type::Integer with limit 4 bytes

app/controllers/posts_controller.rb:47:in `update'

[evazion]

The root problem was that illust id parsing was too loose. Effectively, anything that looked like *.pixiv.net/*/1234.jpg was interpreted as an illust id, which was incorrect for img-sketch.pixiv.net urls. This made saving the post fail because the id was too large to store in the post's pixiv_id field.

I tightened up the parsing. Hopefully this won't break anything. Pixiv has a bunch of legacy url formats that we still have to support because they're still used in old posts.