Matthias Clasen authored Sep 28, 2017 and Behdad Esfahbod committed Dec 19, 2017

We must not look at the instance_id field of the cached ft_face,
since freetype changes it underneath us (if we set the axis values
to match a named instance, the instance_id gets changed to reflect
that). Thankfully, we have the original instance_id stashed away
in the cairo_unscaled_font, so we can just use that to decide if
we are dealing with a named instance or not.

This makes the font variations tests pass.