don't throw for ENOENT on windows in is_canonical_basename
don't throw for ENOENT on windows in is_canonical_basename

Summary:
If an exception escapes the iothread code path uncaught, we'll cancel the root.

For deleted files this is a benign error condition; it's just a TOCTOU.

Reviewed By: sid0

Differential Revision: D4332130

fbshipit-source-id: 9bb8afa0316569b670971475e00a25c97cacde0f

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