Issue

Calling draw() on an empty court breaks the dispute by pushing address(0) in the DK round.votes here because _postDrawCheck() does not validate drawnAddress

Impact

It is impossible to castVote(), even after successfully drawing jurors.

Fix

Fail _postDrawCheck() if drawnAddress is address(0).

Context

This bug was always present but was exacerbated by the fix for #2003 which removed these lines.

Devnet example

Dispute (3 jurors in the oracle court)
Empty draw tx
Successful draw tx
Failing castVote tx