Looking at [the spec](https://xmpp.org/extensions/xep-0004.html#protocol-field)
it seems valid not to have a `var` attribute set, at least for fields of type
`fixed` that is:
> If the element type is anything other than "fixed" (see below), it MUST
> possess a 'var' attribute that uniquely identifies the field in the context
> of the form (if it is "fixed", it MAY possess a 'var' attribute). The element
> MAY possess a 'label' attribute that defines a human-readable name for the field.
XEP-0068 is rather explicit that `FORM_TYPE` fields which are not
`type='hidden'` MUST be ignored (in most cases, see comments inside
the code for exceptions). The previous implementation returned an error
instead (and aborted parsing with that), which is obviously not
"ignoring".
