Incorrect inter-graph edge validation error

[mark-koch]

The following Hugr is expected to be valid

from hugr.build.dfg import Dfg
from hugr import tys, ops

dfg = Dfg(tys.Tuple(tys.Bool, tys.Bool))
bool1, _unused_bool2 = dfg.add_op(ops.UnpackTuple(), *dfg.inputs())
cond = dfg.add_conditional(bool1)
with cond.add_case(0) as case:
    case.set_outputs(bool1)
with cond.add_case(1) as case:
    case.set_outputs(bool1)
dfg.set_outputs(*cond.outputs())

but fails validation with

Error validating HUGR: Missing state order between the external inter-graph source Node(3) and the ancestor of the target Node(4). In an external inter-graph edge from Node(3) (Port(Outgoing, 0)) to Node(7) (Port(Incoming, 0)).

Note that it's important that the external source comes from an UnpackTuple node where the second out-port is not connected. Something seems to go wrong when the builder adds the implicit order edge from the UnpackTuple to the Conditional node. Either the builder does something wrong here or validation handles state order edges incorrectly if the last port of the source node is not connected