refact: update the media item modal loader to load all images until current

src/js/media/routers/manage.js

@@ -39,19 +39,40 @@ var Router = Backbone.Router.extend(/** @lends wp.media.view.MediaFrame.Manage.R
 		var media = wp.media,
 			frame = media.frames.browse,
 			library = frame.state().get('library'),
+			itemId = parseInt( query, 10 ),
 			item;
 
 		// Trigger the media frame to open the correct item.
-		item = library.findWhere( { id: parseInt( query, 10 ) } );
+		item = library.findWhere( { id: itemId } );
 
 		if ( item ) {
 			item.set( 'skipHistory', true );
 			frame.trigger( 'edit:attachment', item );
 		} else {
-			item = media.attachment( query );
+			item = media.attachment( itemId );
 			frame.listenTo( item, 'change', function( model ) {
 				frame.stopListening( item );
 				frame.trigger( 'edit:attachment', model );
+
+				// Load library items in batches until target item is found.
+				var loadMore = function() {
+					var foundItem = library.findWhere( { id: itemId } );
+
+					if ( foundItem ) {
+						// Item found - update edit frame to enable navigation.
+						var editFrame = wp.media.frames.edit;
+						if ( editFrame && editFrame.toggleNav ) {
+							editFrame.model = foundItem;
+							editFrame.toggleNav();
+						}
+					} else if ( library.hasMore() ) {
+						library.more().done( loadMore );
+					}
+				};
+
+				if ( library.hasMore() ) {
+					loadMore();
+				}
 			} );
 			item.fetch();
 		}

src/js/media/views/frame/edit-attachments.js

@@ -240,11 +240,23 @@ EditAttachments = MediaFrame.extend(/** @lends wp.media.view.MediaFrame.EditAtta
 	},
 
 	hasNext: function() {
-		return ( this.getCurrentIndex() + 1 ) < this.library.length;
+		var currentIndex = this.getCurrentIndex();
+
+		// Ensure model is in library collection before allowing navigation
+		if ( -1 === currentIndex ) {
+			return false;
+		}
+		return ( currentIndex + 1 ) < this.library.length;
 	},
 
 	hasPrevious: function() {
-		return ( this.getCurrentIndex() - 1 ) > -1;
+		var currentIndex = this.getCurrentIndex();
+
+		// Ensure model is in library collection before allowing navigation
+		if ( -1 === currentIndex ) {
+			return false;
+		}
+		return ( currentIndex - 1 ) > -1;
 	},
 	/**
 	 * Respond to the keyboard events: right arrow, left arrow, except when