avoid stack use after return
avoid stack use after return

Summary:
it's only valid to capture a reference to the settle callback in here,
the other captures have to be by value.

Reviewed By: strager

Differential Revision: D10080989

fbshipit-source-id: 3797585d65fe109e5be0e054d585158868a3f7c4

nodakai/watchman,wez/watchman,facebook/watchman,facebook/watchman,wez/watchman,wez/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,wez/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,wez/watchman,facebook/watchman,wez/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,wez/watchman,wez/watchman