utils.rb in ngt-0.4.1

- old
+ new

@@ -2,10 +2,13 @@
   module Utils
     # private
     def self.ffi(method, *args)
       res = FFI.send(method, *args)
       message = FFI.ngt_get_error_string(args.last)
-      raise Error, message unless message.empty?
+      unless message.empty?
+        FFI.ngt_clear_error_string(args.last)
+        raise Error, message
+      end
       res
     end
 
     private
 