Fix shadow-uncaptured-local compilation error in ServerGeneratorStream-inl.h
Fix shadow-uncaptured-local compilation error in ServerGeneratorStream-inl.h

Summary: This warning breaks some contbuild, see task.

Reviewed By: yfeldblum

Differential Revision: D28158490

fbshipit-source-id: eab2b07e01777a8f130dcfcb36f42b32ae2ebb65

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift