fix: fix `search.js` two BUGs: `404` and `handlePostContent is undefined`

[wangliang181230]

• [x] 1. url is wrong if multiple contents are on the same site, example: https://xxxxx/docs/ and https://xxxxx/blog/
• [x] 2. when the token.text is undefined, handlePostContent is undefined too at line 217 https://github.com/docsifyjs/docsify/blob/develop/src/plugins/search/search.js#L217

Summary

What kind of change does this PR introduce?

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• [ ] Related documentation has been updated if needed
• [ ] Related tests have been updated or tests have been added

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• [x] No

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• [ ] Firefox
• [ ] Safari
• [ ] Edge
• [ ] IE

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[wangliang181230]

Anybody here?