unexpected twitter:card without image

[Mister-Hope]

Page settings: no setting, default md file, text only, without image.

  [ 'meta', { name: 'twitter:card', content: 'summary_large_image' } ],
  [ 'meta', { name: 'twitter:image:alt', content: 'Chaldea' } ]

These two are always added even twitterId not set and without image. And og:image is also not added.
So I think it's better not to append twitter card tag when both are empty.
og:description is not added too, not sure where you parse this from.

Furthermore, when there is no image on this page, It can be fallback to site icon, and description fallback to <meta name="description">

Originally posted by @narumishi in #1587