Fret diagram: strings with no X or O display as ? on Linux
Linux only, apparently, and maybe not all Linux distrubtions. But fret diagrams are rendering in the palette and on the score with "?" characters on the strings with no X or O. That's because we are trying to draw a null character in FreeSans, and I guess it's not always defined. It worked in some previous release, not sure when it broke, but no matter, cause and possible fixes are obvious enough.