Fix pointer arrow in Installer icon

This is probs an issue with the Pocillo icon theme, but here’s the 19.10 installed:

The black arrow should be white, as I’m using stock Pocillo, which uses a dark element for that. The fix should be either a gtk theme hack to make that part’s background white, or an icon hack to make the arrow white.
UB should appear polished to new users :stuck_out_tongue:

And when nobody responds…