Editor link autocomplete suggestions: no fallback title displayed for posts with no title

[afercia]

When inserting a link in a post, the links suggestions list doesn't show any fallback title for posts with no title. There's just an empty space followed by the post date:

Worth noting the "Link options" modal does display a fallback title for that same post, and it's the string (no title) already used in other places in core:

[afercia]

42664.diff​ is a first pass, I guess it is necessary to check for window.wpLinkL10n as that check is done in other parts too, but I'm not so sure why. Any feedback welcome.

[afercia]

In 42425:

Editor: Link suggestions: add fallback title for posts with no title.

Fixes #42664.

[afercia]

Reopening for 4.9.2 consideration.

[SergeyBiryukov]

In 42439:

Editor: Link suggestions: add fallback title for posts with no title.

Props afercia.
Merges [42425] to the 4.9 branch.
Fixes #42664.