[gui][c] Fix unmarshal when corrupted dfss json

Fix #10

dfssc/common/file.go

@@ -2,6 +2,7 @@ package common
 
 import (
 	"encoding/json"
+	"errors"
 
 	"dfss/dfssp/contract"
 )
@@ -15,5 +16,9 @@ func UnmarshalDFSSFile(data []byte) (*contract.JSON, error) {
 		return nil, err
 	}
 
+	if c.File == nil {
+		return nil, errors.New("empty file description")
+	}
+
 	return c, nil
 }

gui/showcontract/showcontract.go

@@ -2,9 +2,9 @@
 package showcontract
 
 import (
-	"encoding/json"
 	"io/ioutil"
 
+	"dfss/dfssc/common"
 	"dfss/dfssp/contract"
 	"github.com/visualfc/goqt/ui"
 )
@@ -49,8 +49,7 @@ func Load(filename string) *contract.JSON {
 		return nil
 	}
 
-	contract := new(contract.JSON)
-	err = json.Unmarshal(data, contract)
+	contract, err := common.UnmarshalDFSSFile(data)
 	if err != nil {
 		return nil
 	}