THRIFT-1119. csharp: TJSONProtocol fails to UTF8 decode strings

Patch: guoyunfeng

git-svn-id: https://svn.apache.org/repos/asf/thrift/trunk@1086262 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/csharp/src/Protocol/TJSONProtocol.cs b/lib/csharp/src/Protocol/TJSONProtocol.cs
index e2834f8..7c88f0f 100644
--- a/lib/csharp/src/Protocol/TJSONProtocol.cs
+++ b/lib/csharp/src/Protocol/TJSONProtocol.cs
@@ -1058,7 +1058,7 @@
 
 		public override String ReadString()
 		{
-			return ReadJSONString(false).ToString();
+			return utf8Encoding.GetString(ReadJSONString(false));
 		}
 
 		public override byte[] ReadBinary()