Fix a JavaScript error when the media edit screen is loaded directly via a url such as `/wp-admin/post.php?post={post_id}&action=edit&image-editor`. Add a check in `imgLoaded` for `this.hold.sizer` which is set up during initialization and required for the cropping tool. Call `init` if this is undefined.
Props NoseGraze.
Fixes#38138.
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git-svn-id: http://core.svn.wordpress.org/trunk@39957 1a063a9b-81f0-0310-95a4-ce76da25c4cd