From: Stefan Sayer <stefan.sayer@googlemail.com>
Date: Fri, 31 Jul 2015 01:12:00 +0200
Subject: [PATCH] b/f:core:json: fix printing special characters

(cherry picked from commit 7793cf157f7d8971db4ca3feb08900b4281c1802)

diff --git a/core/jsonArg.cpp b/core/jsonArg.cpp
index 78cfc8ca..f49186fa 100644
--- a/core/jsonArg.cpp
+++ b/core/jsonArg.cpp
@@ -94,7 +94,7 @@ string str2json(const char* str, size_t len)
 	// (I hope I am not misunderstanding something.)
       default:{
 	if (*c < ' ') 
-	  result += "\\u00" + hex_chars[*c >> 4] + hex_chars[*c & 0xf];
+	  result += "\\u00" + string() + hex_chars[*c >> 4] + string() + hex_chars[*c & 0xf];
 	else 
 	  result += *c;
       } break;