Fix unused variable compiler warning
Fix unused variable compiler warning

Summary: Closes https://github.com/facebook/fbthrift/pull/163

Reviewed By: juchem

Differential Revision: D3581881

Pulled By: alandau

fbshipit-source-id: f64c63b5ea6b998e0475e25db09aaf21509aca07

LinusU/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,facebook/fbthrift,LinusU/fbthrift,LinusU/fbthrift,facebook/fbthrift,facebook/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,facebook/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,facebook/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,facebook/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift