[autocomplete] fix logged reason for null/void autocomplete failure
[autocomplete] fix logged reason for null/void autocomplete failure

Summary: D18340917 accidentally (as far as I can tell) made `null`/`void` fall through to the `FailureAnyType` case instead of `FailureNullishType`.

Reviewed By: nmote

Differential Revision: D18476438

fbshipit-source-id: c9d2b814dd34e4cd10851b2f4511c5725f0d0bfd

samwgoldman/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,mroch/flow,samwgoldman/flow,mroch/flow,mroch/flow,mroch/flow,samwgoldman/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow