Skip reallocation in shrink_to_fit for empty fbvector
Skip reallocation in shrink_to_fit for empty fbvector

Reviewed By: philippv

Differential Revision: D2696314

fb-gh-sync-id: 105de2d99bb9f5ac82310e37f9302022c103befc

Orvid/folly,juniway/folly,floxard/folly,rklabs/folly,brunomorishita/folly,facebook/folly,floxard/folly,mqeizi/folly,Hincoin/folly,Hincoin/folly,mqeizi/folly,sonnyhu/folly,Orvid/folly,Hincoin/folly,rklabs/folly,juniway/folly,mqeizi/folly,rklabs/folly,Orvid/folly,alexst07/folly,sonnyhu/folly,charsyam/folly,brunomorishita/folly,charsyam/folly,juniway/folly,sonnyhu/folly,floxard/folly,Orvid/folly,facebook/folly,charsyam/folly,facebook/folly,alexst07/folly,brunomorishita/folly,sonnyhu/folly,floxard/folly,mqeizi/folly,Hincoin/folly,floxard/folly,facebook/folly,alexst07/folly,rklabs/folly,brunomorishita/folly,rklabs/folly,juniway/folly,mqeizi/folly,Hincoin/folly,sonnyhu/folly,alexst07/folly,alexst07/folly,brunomorishita/folly,juniway/folly,facebook/folly,Orvid/folly,charsyam/folly