Also return a different code for a NULL pointer, vs a failed call.

BUG=477701

Change-Id: Ib0584371d51b99760e80ce5481a1e72e1ec673e0
Reviewed-on: https://chromium-review.googlesource.com/267753Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>