Tidy Democracy (#10867)

* add test

* Assorted refactorings

* complete test

* saturating math

* final check

* use `default`

Co-authored-by: Gav Wood <gavin@parity.io>

substrate/frame/democracy/src/vote.rs

@@ -183,7 +183,7 @@ impl<Balance: Saturating + Ord + Zero + Copy, BlockNumber: Ord + Copy + Zero, Ac
 		match self {
 			Voting::Direct { votes, prior, .. } =>
 				votes.iter().map(|i| i.1.balance()).fold(prior.locked(), |a, i| a.max(i)),
-			Voting::Delegating { balance, .. } => *balance,
+			Voting::Delegating { balance, prior, .. } => *balance.max(&prior.locked()),
 		}
 	}
 
@@ -199,4 +199,11 @@ impl<Balance: Saturating + Ord + Zero + Copy, BlockNumber: Ord + Copy + Zero, Ac
 		*d = delegations;
 		*p = prior;
 	}
+
+	pub fn prior(&self) -> &PriorLock<BlockNumber, Balance> {
+		match self {
+			Voting::Direct { prior, .. } => prior,
+			Voting::Delegating { prior, .. } => prior,
+		}
+	}
 }