fix paych vouchers make check (#538)

Signed-off-by: turuslan <[email protected]>

Author: turuslan

core/paych/vouchers.cpp

@@ -174,10 +174,11 @@ namespace fc::paych_vouchers {
     std::unique_lock lock{mutex};
     OUTCOME_TRY(ctx, loadCtx(paych));
     OUTCOME_TRY(laneStates(ctx));
-    if (amount <= laneRedeem(ctx, lane)) {
+    const TokenAmount delta{amount - laneRedeem(ctx, lane)};
+    if (delta <= 0) {
       return ERROR_TEXT("PaychVouchers::make voucher adds no value");
     }
-    if (*ctx.total + amount > ctx.balance) {
+    if (*ctx.total + delta > ctx.balance) {
       return ERROR_TEXT("PaychVouchers::make insufficient balance");
     }
     SignedVoucher voucher;

test/core/paych/vouchers_test.cpp

@@ -124,5 +124,7 @@ namespace fc::paych_vouchers {
     checkFails(voucher);
     EXPECT_EQ(addOk(voucher, voucher.amount), 0);
     makeFails(1, balance - voucher.amount + 1);
+    makeFails(0, voucher.amount);
+    makeOk(0, voucher.amount + 1);
   }
 }  // namespace fc::paych_vouchers