Refactors error handling should map() fail to avoid crashing
during a device error event.

BUG=angleproject:2284

Change-Id: Ib1eb676860fa5c3a81e523f49aab82b7e6700f73
Reviewed-on: https://chromium-review.googlesource.com/826485Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>