It is possible for some hardware to not support multisampling on any
texture formats which results in an empty sample set for all formats.

BUG=angleproject:2242

Change-Id: I8148c781ec22ec02562b6a8b5d1b966c6f13915e
Reviewed-on: https://chromium-review.googlesource.com/766568Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>