It was occasioned by my switching away from using a 4K TV as my monitor and replacing it with two 1920x1200 monitors in a dual-screen setup. Since I had never used a dual screen display before, I had not realised that when Giocoso is asked to display album art as a new recording plays, it would break when confronted with the decision as to which monitor it would display the art on!
The fix is now in place. It brings Giocoso up to version 1.03, and when album art is displayed, it is displayed on the primary monitor. Similarly, it's the primary monitor's screen resolution that is used to calculate where, precisely, to place the album art display window. In my case, both monitors use the same screen resolution, so that's not actually an issue, but if you had a 1900x1200 and a 1600x1440 monitor side-by-side, knowing to use the 1900 horizontal screen resolution to define 'middle' and not the 1600 one makes a difference!
Anyway, if you don't have a dual monitor setup, you needn't particularly worry about applying the update to Giocoso (but it won't harm you if you do, either). But if you want to apply the update, the standard approach applies: just issue the command
...and the new version will be automatically downloaded and applied for you (once the sudo password has been supplied, of course!)