Fix ignored errors from Unstringify. (#160)

* check forinvalid properties

* fix typo

Author: brianterry

cfn/encoding/unmarshal.go

@@ -7,12 +7,16 @@ import (
 // Unmarshal converts stringified-JSON into the passed-in type
 func Unmarshal(data []byte, v interface{}) error {
 	var dataMap map[string]interface{}
-	err := json.Unmarshal(data, &dataMap)
+	var err error
+	err = json.Unmarshal(data, &dataMap)
 	if err != nil {
 		return err
 	}
 
-	Unstringify(dataMap, v)
+	err = Unstringify(dataMap, v)
+	if err != nil {
+		return err
+	}
 
 	return nil
 }