routing: fix race condition in TestUpdatePaymentState

The test cases in `TestUpdatePaymentState` run in parallel. One of the
parameters is a pointer and the value to the struct it points to gets
modified during the test.

The race condition was introduced in 8d49dfb07e
To test the fix run from the main folder `go test  ./routing/. -race`
before this fix and after.

routing/payment_lifecycle_test.go

@@ -938,40 +938,14 @@ func TestUpdatePaymentState(t *testing.T) {
 
 	// paymentHash is the identifier on paymentLifecycle.
 	paymentHash := lntypes.Hash{}
+	preimage := lntypes.Preimage{}
+	failureReasonError := channeldb.FailureReasonError
 
 	// TODO(yy): make MPPayment into an interface so we can mock it. The
 	// current design implicitly tests the methods SendAmt, TerminalInfo,
 	// and InFlightHTLCs on channeldb.MPPayment, which is not good. Once
 	// MPPayment becomes an interface, we can then mock these methods here.
 
-	// SentAmt returns 90, 10
-	// TerminalInfo returns non-nil, nil
-	// InFlightHTLCs returns 0
-	var preimage lntypes.Preimage
-	paymentSettled := &channeldb.MPPayment{
-		HTLCs: []channeldb.HTLCAttempt{
-			makeSettledAttempt(100, 10, preimage),
-		},
-	}
-
-	// SentAmt returns 0, 0
-	// TerminalInfo returns nil, non-nil
-	// InFlightHTLCs returns 0
-	reason := channeldb.FailureReasonError
-	paymentFailed := &channeldb.MPPayment{
-		FailureReason: &reason,
-	}
-
-	// SentAmt returns 90, 10
-	// TerminalInfo returns nil, nil
-	// InFlightHTLCs returns 1
-	paymentActive := &channeldb.MPPayment{
-		HTLCs: []channeldb.HTLCAttempt{
-			makeActiveAttempt(100, 10),
-			makeFailedAttempt(100, 10),
-		},
-	}
-
 	testCases := []struct {
 		name     string
 		payment  *channeldb.MPPayment
@@ -992,16 +966,31 @@ func TestUpdatePaymentState(t *testing.T) {
 		{
 			// Test that when the sentAmt exceeds totalAmount, the
 			// error is returned.
-			name:              "amount exceeded error",
-			payment:           paymentSettled,
+			name: "amount exceeded error",
+			// SentAmt returns 90, 10
+			// TerminalInfo returns non-nil, nil
+			// InFlightHTLCs returns 0
+			payment: &channeldb.MPPayment{
+				HTLCs: []channeldb.HTLCAttempt{
+					makeSettledAttempt(100, 10, preimage),
+				},
+			},
 			totalAmt:          1,
 			shouldReturnError: true,
 		},
 		{
 			// Test that when the fee budget is reached, the
 			// remaining fee should be zero.
-			name:     "fee budget reached",
-			payment:  paymentActive,
+			name: "fee budget reached",
+			payment: &channeldb.MPPayment{
+				// SentAmt returns 90, 10
+				// TerminalInfo returns nil, nil
+				// InFlightHTLCs returns 1
+				HTLCs: []channeldb.HTLCAttempt{
+					makeActiveAttempt(100, 10),
+					makeFailedAttempt(100, 10),
+				},
+			},
 			totalAmt: 1000,
 			feeLimit: 1,
 			expectedState: &paymentState{
@@ -1014,8 +1003,15 @@ func TestUpdatePaymentState(t *testing.T) {
 		{
 			// Test when the payment is settled, the state should
 			// be marked as terminated.
-			name:     "payment settled",
-			payment:  paymentSettled,
+			name: "payment settled",
+			// SentAmt returns 90, 10
+			// TerminalInfo returns non-nil, nil
+			// InFlightHTLCs returns 0
+			payment: &channeldb.MPPayment{
+				HTLCs: []channeldb.HTLCAttempt{
+					makeSettledAttempt(100, 10, preimage),
+				},
+			},
 			totalAmt: 1000,
 			feeLimit: 100,
 			expectedState: &paymentState{
@@ -1028,8 +1024,13 @@ func TestUpdatePaymentState(t *testing.T) {
 		{
 			// Test when the payment is failed, the state should be
 			// marked as terminated.
-			name:     "payment failed",
-			payment:  paymentFailed,
+			name: "payment failed",
+			// SentAmt returns 0, 0
+			// TerminalInfo returns nil, non-nil
+			// InFlightHTLCs returns 0
+			payment: &channeldb.MPPayment{
+				FailureReason: &failureReasonError,
+			},
 			totalAmt: 1000,
 			feeLimit: 100,
 			expectedState: &paymentState{