Using unique pointers to avoid memory leak in json for expressions

This will delete language pointer created by get_language_from_mode
when the object goes out of scope.
This prevents memory leaks when using json output.

Author: romainbrenguier

src/util/json_expr.cpp

@@ -6,6 +6,8 @@ Author: Peter Schrammel
 
 \*******************************************************************/
 
+#include <memory>
+
 #include "namespace.h"
 #include "expr.h"
 #include "json.h"
@@ -274,14 +276,14 @@ json_objectt json(
         type.id()==ID_c_bit_field?type.subtype():
         type;
 
-      languaget *lang;
+      std::unique_ptr<languaget> lang;
       if(mode==ID_unknown)
-        lang=get_default_language();
+        lang=std::unique_ptr<languaget>(get_default_language());
       else
       {
-        lang=get_language_from_mode(mode);
+        lang=std::unique_ptr<languaget>(get_language_from_mode(mode));
         if(!lang)
-          lang=get_default_language();
+          lang=std::unique_ptr<languaget>(get_default_language());
       }
 
       std::string type_string;