Make widget customizer code pass JSHint.

Fixes #27298.



git-svn-id: https://develop.svn.wordpress.org/trunk@27436 602fd350-edb4-49c9-b593-d223f7449a82
Revisions: Restore [24929] which was reverted in [26072].

props avryl.
fixes #27267.

git-svn-id: https://develop.svn.wordpress.org/trunk@27437 602fd350-edb4-49c9-b593-d223f7449a82