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.


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git-svn-id: http://core.svn.wordpress.org/trunk@27365 1a063a9b-81f0-0310-95a4-ce76da25c4cd