fix: ssr treats all anchor links as external

[Jille]

https://github.com/quasarframework/quasar-ui-qmarkdown/commit/556ff29af89b57aa58b74525506476fb405ddd6f made it skip the anchor expanding when we're in SSR mode. However, that means that a later check will mark it as an external link (which adds the external-link icon)

This resolves the difference between the SSG (and probably SSR) and the browsers rendering