ProgramGL: correctly copy sampler uniforms
ProgramGL: correctly copy sampler uniforms

BUG=angleproject:1570

Change-Id: Ic39f5f1ff8f565b2876fdfc8d738a50f24b911b6
Reviewed-on: https://chromium-review.googlesource.com/402930
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

ecoal95/angle,ppy/angle,MSOpenTech/angle,ppy/angle,ecoal95/angle,MSOpenTech/angle,ecoal95/angle,ppy/angle,ecoal95/angle,MSOpenTech/angle,MSOpenTech/angle,ecoal95/angle,ppy/angle