Add a test for adding alpha to a large image
Add a test for adding alpha to a large image

This is prone to segfaults when we are not careful.

Distrotech/gdk-pixbuf,Distrotech/gdk-pixbuf,GNOME/gdk-pixbuf,Distrotech/gdk-pixbuf,GNOME/gdk-pixbuf,Distrotech/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,Distrotech/gdk-pixbuf