Correctly access the nonce to save attachment fields. Fixes firing attachment_fields_to_save.

Props koopersmith
fixes #22577


git-svn-id: https://develop.svn.wordpress.org/trunk@22842 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/js/media-models.js

@@ -269,7 +269,7 @@ window.wp = window.wp || {};
 
 			return media.post( 'save-attachment-compat', _.defaults({
 				id:     this.id,
-				nonce:  l10n.saveAttachmentNonce
+				nonce:  media.model.settings.saveAttachmentNonce
 			}, data ) ).done( function( resp, status, xhr ) {
 				model.set( model.parse( resp, xhr ), options );
 			});