False-positive Device table warnings in variable fonts

[Hoolean]

Hello! : )

When Font Validator tests a variable font, it sometimes produces false-positive warnings for Device table values.

Variable fonts may repurpose Device tables as VariationIndex tables, for which 'startSize' and 'endSize' become 'deltaSetOuterIndex' and 'deltaSetInnerIndex' respectively. While Font Validator checks the format of the table before doing most checks, the size fields are interpreted prior to this and – as they contain indices – are often seen as invalid.

This bug can probably be resolved by moving the format check to encompass earliest parts of the function, which the spec suggests here as a means of handling this distinction.

[HinTak]

Sounds like a good issue for somebody to get familiar with the code and send a possible patch.