Eo: eo_do now returns called func's value + default ret fix.

Eo: eo_do now returns called func's value + default ret fix.

It's now completely valid to do:
a = eo_do(obj, a_get());

or:
b = eo_do(obj, a_set(1), b_get());

Also, the default return value for eo2 functions is now also returned
when the object is invalid, not just when the object does not match
class.

It's a small refactor that fixed both issues at once.

@feature
@fix