Fix stack use after return in Observer.ObservableLockInversion
Fix stack use after return in Observer.ObservableLockInversion

Reviewed By: praihan

Differential Revision: D32297368

fbshipit-source-id: a58c7805d396cc30c0d82a49d5998e2f9d8a799a

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly