glue: fix memory leak in conv_flags_to_str

The function 'bolt_flags_class_to_string' returns a dynamically
allocated string. This was previously not freed, creating a memory
leak. Its ownership is now correctly transferred to the GVariant
instead.

common/bolt-glue.c

@@ -319,7 +319,7 @@ conv_flags_to_str (BoltWireConv *conv,
                    GError      **error)
 {
   GParamSpecFlags *fs;
-  const char *str;
+  char *str;
   guint uv;
 
   fs = G_PARAM_SPEC_FLAGS (conv->prop_spec);
@@ -330,7 +330,7 @@ conv_flags_to_str (BoltWireConv *conv,
   if (str == NULL)
     return NULL;
 
-  return g_variant_new_string (str);
+  return g_variant_new_take_string (str);
 }
 
 static gboolean