[nostalgia/studio] Get Undo/Redo working

src/nostalgia/studio/lib/editor.hpp

@@ -32,6 +32,7 @@ class NOSTALGIASTUDIO_EXPORT Editor: public Widget {
 		[[nodiscard]]
 		virtual ox::String itemName() const = 0;
 
+		[[nodiscard]]
 		virtual ox::String itemDisplayName() const;
 
 		virtual void cut();
@@ -42,6 +43,14 @@ class NOSTALGIASTUDIO_EXPORT Editor: public Widget {
 
 		virtual void exportFile();
 
+		/**
+		 * Returns the undo stack holding changes to the item being edited.
+		 */
+		[[nodiscard]]
+		virtual UndoStack *undoStack() noexcept {
+			return nullptr;
+		}
+
 		void close();
 
 		/**
@@ -58,12 +67,6 @@ class NOSTALGIASTUDIO_EXPORT Editor: public Widget {
 		[[nodiscard]]
 		bool unsavedChanges() const noexcept;
 
-		/**
-		 * Returns the undo stack holding changes to the item being edited.
-		 */
-		[[nodiscard]]
-		UndoStack *undoStack();
-
 		void setExportable(bool);
 
 		[[nodiscard]]