Fix SlideShare oEmbed regex.

props kovshenin.
fixes #28380.

git-svn-id: https://develop.svn.wordpress.org/trunk@28597 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fourteen: Avoid passing an empty string to document.getElementById().

props nabil_kadimi.
fixes #28340.

git-svn-id: https://develop.svn.wordpress.org/trunk@28598 602fd350-edb4-49c9-b593-d223f7449a82