zuse: if empty, unpack header into empty list
Previously, would give a ~[{}] for the '' header. This makes it parse
that as "no entries" rather than "one entry without data".
++ pairs
%+ cook
~(gas by *(map @t @t))
- %+ more (ifix [. .]:(star ace) mic)
+ %+ most (ifix [. .]:(star ace) mic)
;~(plug token ;~(pose ;~(pfix tis value) (easy '')))
::
++ value
