Fix invalid generated sampling functions in HLSL output In some generated shaders, "levels" would be read before it is assigned by GetDimensions when clamping mip level to valid range. Fix these cases. BUG=angleproject:1092 TEST=dEQP-GLES3.functional.shaders.texture_functions.* (12 tests start passing) Change-Id: I9fce8d378606738e5172673d222bce7968e26789 Reviewed-on: https://chromium-review.googlesource.com/312022 Tryjob-Request: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com>