Menu widget line-h.png border issue, w/ fix from breeze

Original bug report:

• https://bugs.kde.org/show_bug.cgi?id=404045

Problematic line:

• https://gitlab.manjaro.org/artwork/themes/breath-gtk/blob/master/Breath/gtk-2.0/widgets/menu#L40

See also:

• https://github.com/ahlstromcj/sequencer64/issues/126
• https://github.com/ahlstromcj/sequencer64/issues/154
• https://github.com/ahlstromcj/sequencer64/issues/185