fix access-after-free bug in ProducerConsumerQueueTest
fix access-after-free bug in ProducerConsumerQueueTest

Summary: This bug causes failure when the test is run under ASAN.

Reviewed By: meyering

Differential Revision: D3229494

fb-gh-sync-id: a43c8332cc45f7892ac86cd0abb799616bca7779
fbshipit-source-id: a43c8332cc45f7892ac86cd0abb799616bca7779

facebook/folly,rklabs/folly,rklabs/folly,brunomorishita/folly,Orvid/folly,charsyam/folly,charsyam/folly,floxard/folly,facebook/folly,Orvid/folly,mqeizi/folly,floxard/folly,brunomorishita/folly,floxard/folly,rklabs/folly,rklabs/folly,brunomorishita/folly,charsyam/folly,mqeizi/folly,charsyam/folly,facebook/folly,brunomorishita/folly,facebook/folly,floxard/folly,mqeizi/folly,rklabs/folly,mqeizi/folly,mqeizi/folly,facebook/folly,floxard/folly,Orvid/folly,brunomorishita/folly,Orvid/folly,Orvid/folly