The Image Editor should apply changes to custom image sizes by checking `$_wp_additional_image_sizes` for `$size` in `wp_save_image()` before arbitrarily going to the options table.

Props Otto42, SergeyBiryukov.
Fixes #19889.



git-svn-id: https://develop.svn.wordpress.org/trunk@27522 602fd350-edb4-49c9-b593-d223f7449a82