Euro character (€) not working (console error)

[Dunos]

While trying to use the rich-text-editor with the € symbol, it breaks the code .

To reproduce this:

1. Open the demo site: http://digabi.github.io/rich-text-editor/
2. Focus the input box
3. Use the Ctrl+E shortcut (or click the "Lisää kaava" button on the toolbar)
4. Enter the "€" symbol
5. Check the console for error "Uncaught TypeError: Cannot read properties of null (reading '4')"