Don't allocate name strings for empty symbols This removes unnecessary memory allocations. BUG=angleproject:2267 TEST=angle_unittests Change-Id: Ide575ea19ab2f8e9fc93092490f1352efa6024a3 Reviewed-on: https://chromium-review.googlesource.com/817415 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Corentin Wallez <cwallez@chromium.org>