This commit removes an unnecessary `empty()` check, where the `$class` variable is primed at the top of the `foreach` loop and will always be a non-empty array.
To maintain readability of the source of the `$class` attribute without the unnecessary `empty()` check, the resulting variable has been renamed to `$class_attr`, instead of reusing the array.
Follow-up to [8923], [15491].
Props justlevine.
See #52217.
Built from https://develop.svn.wordpress.org/trunk@60132
git-svn-id: http://core.svn.wordpress.org/trunk@59468 1a063a9b-81f0-0310-95a4-ce76da25c4cd
d38b0e164c