Array size must be greater than zero according to the ESSL 3.00.6
spec.

BUG=angleproject:1602
TEST=angle_unittests

Change-Id: I1fa54b143bc821583822cbc5139464cdd058b6c1
Reviewed-on: https://chromium-review.googlesource.com/407257
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>