Always use configured voting account when mixing

The comments suggested that this was the intended behavior, but the voting
account option was only being considered when UseVotingAccount (allowing the
option to be used in non-mixing situations) was true, and mixed ticketbuying
was not setting this value.

wallet/createtx.go

@@ -1510,13 +1510,13 @@ func (w *Wallet) purchaseTickets(ctx context.Context, op errors.Op,
 
 		var addrVote stdaddr.StakeAddress
 
-		// If req.UseVotingAccount is true, derive the submission
-		// script's address from the voting account. This is intended
-		// to be used with a special account type. The signing address
-		// for the same index is saved to the database. That address is
-		// later used to sign messages sent to a vspd related to this
-		// ticket.
-		if req.UseVotingAccount {
+		// If req.Mixing or req.UseVotingAccount is true, derive the
+		// submission script's address from the voting account. This
+		// is intended to be used with a special account type. The
+		// signing address for the same index is saved to the
+		// database. That address is later used to sign messages sent
+		// to a vspd related to this ticket.
+		if req.Mixing || req.UseVotingAccount {
 			var idx uint32
 			addrVote, idx, err = stakeAddrFunc(op, req.VotingAccount, 1)
 			if err != nil {

wallet/wallet.go

@@ -1545,7 +1545,7 @@ type PurchaseTicketsRequest struct {
 	SourceAccount    uint32
 	MinConf          int32
 	Expiry           int32
-	VotingAccount    uint32 // Used when Mixing == true
+	VotingAccount    uint32 // Used when Mixing == true || UseVotingAccount == true
 	UseVotingAccount bool   // Forces use of supplied voting account.
 	DontSignTx       bool