MathInfo should not assume font.info object has "guidelines" attribute

[LettError]

A FontParts font.info object does not have a guidelines attribute.
https://github.com/typesupply/fontMath/blob/master/Lib/fontMath/mathInfo.py#L17

[typemytype]

there is some 'trickery' going on here

see https://github.com/robofab-developers/fontParts/blob/master/Lib/fontParts/base/info.py#L196-L199