data.tags.split fix

[youliao]

Tags is empty string:

https://konachan.com/post.json?tags=id:38805

Example:
const results = await Booru.search("konac", "id:38805");

Then throw error:

TypeError: Cannot read properties of undefined (reading 'split')
at getTags (/usr/src/node_modules/booru/dist/structures/Post.js:1:900)
at new Post (/usr/src/node_modules/booru/dist/structures/Post.js:1:2165)
at /usr/src/node_modules/booru/dist/boorus/Booru.js:1:2633
at Array.map ()
at Booru.parseSearchResult (/usr/src/node_modules/booru/dist/boorus/Booru.js:1:2625)
at Booru.search (/usr/src/node_modules/booru/dist/boorus/Booru.js:1:927)
at runMicrotasks ()
at processTicksAndRejections (node:internal/process/task_queues:96:5)...