Update token_contract.go, checking the input params > 0 in function sub().

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

Author: yjwxfq

token-erc-20/chaincode-go/chaincode/token_contract.go

@@ -719,13 +719,15 @@ func checkInitialized(ctx contractapi.TransactionContextInterface) (bool, error)
 // sub two number checking for overflow
 func sub(b int, q int) (int, error) {
 
-	// Check overflow
+	// sub two number checking 
+	if q <= 0 {
+		return 0, fmt.Errorf("Error: the subtraction number is %d, it should be greater than 0", q)
+	}
+	if b < q {
+		return 0, fmt.Errorf("Error: the number %d is not enough to be subtracted by %d", b, q)
+	}
 	var diff int
 	diff = b - q
 
-	if (diff < b || diff < -q) == (b >= 0 && q <= 0) {
-		return 0, fmt.Errorf("Math: Subtraction overflow occurred  %d - %d", b, q)
-	}
-
 	return diff, nil
 }