cropgtk.py version uses monitor(0), not 'current' monitor

[Ndolam]

cropgtk.py contains the following code:

display = gdk.Display().get_default()
wa = display.get_monitor(0).get_workarea()

However, rather than hard-coding 0 in get_monitor(), I think it should use the monitor where the mouse is.
(Issue: I have a laptop with a 15.6" 1080p screen connected to a large 4K external monitor, and even when I am working on the large monitor, the code uses the size of my laptop screen to scale the initial display. This is not convenient.)

I took a quick look at some docs, but being neither a Python programmer nor a Gtk programmer, it wasn't obvious what incantation is needed to select the monitor where the mouse is. Anyone here know enough Gtk to fix this?