Synthesis SLNT is hardcoded as 14 for the Italic style

[fredizzimo]

When loading a Vairable font like Monaspace Xenon Var with the an italic style the Synthesis setting for SLNT gets wrongly set to 14.
StyleProperty::FontStack(FontStack::Source("Monaspace Xenon Var"))
StyleProperty::FontStyle(FontStyle::Italic)

In that particular font the value should be negative, -11 for the Italic style, and positive values are invalid, so the end result is that the font is rendered as normal instead of slanted and italic.

OS: Linux