Slideshow: long titles display a   at the end

#### Steps to reproduce the issue
1. Create/edit a post
2. Add a gallery with a few images
3. Add a long title (not a caption) to those images. Something like:
> A really long title, just to check if it breaks in the slideshow
4. Visit the gallery
5. Hover over the image

#### What I expected
To see the title correctly.

#### What happened instead
I'm seeing a ` ` similar to the one it's available with the `widont` function. I'm assuming it may be related to the [widont](https://vip.wordpress.com/functions/widont/) since it only applies to titles, not to the `alt`. Both `title` and `alt` were added in #1095.

#### Screenshots

#user-report
1164472-zen

No file or test is named in the issue. Reproduce the gallery slideshow case, then trace how image titles are rendered and where the widont function is applied; the fix is done when a long title displays without a literal   while the alt text remains correct.

Written by the indexing model from the issue text.