Fix GetUniform validation.
Fix GetUniform validation.

We were missing a check for an out-of-bounds Uniform, which could
cause us to miss an error and also give assertion failures.

BUG=angle:571

Change-Id: I844658a82ce13ea179a2358a202733c54bc2c0c7
Reviewed-on: https://chromium-review.googlesource.com/212934
Tested-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

bsergean/angle,crezefire/angle,mrobinson/rust-angle,mikolalysenko/angle,ghostoy/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,nandhanurrevanth/angle,larsbergstrom/angle,mybios/angle,mlfarrell/angle,bsergean/angle,mikolalysenko/angle,mybios/angle,MIPS/external-chromium_org-third_party-angle,jgcaaprom/android_external_chromium_org_third_party_angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,jgcaaprom/android_external_chromium_org_third_party_angle,ghostoy/angle,mikolalysenko/angle,mrobinson/rust-angle,android-ia/platform_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,ghostoy/angle,crezefire/angle,csa7mdm/angle,domokit/waterfall,nandhanurrevanth/angle,nandhanurrevanth/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,mrobinson/rust-angle,bsergean/angle,nandhanurrevanth/angle,MIPS/external-chromium_org-third_party-angle,csa7mdm/angle,ppy/angle,vvuk/angle,mikolalysenko/angle,MSOpenTech/angle,MSOpenTech/angle,mlfarrell/angle,mrobinson/rust-angle,larsbergstrom/angle,vvuk/angle,ppy/angle,larsbergstrom/angle,mlfarrell/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,crezefire/angle,ghostoy/angle,larsbergstrom/angle,android-ia/platform_external_chromium_org_third_party_angle,ppy/angle,mlfarrell/angle,android-ia/platform_external_chromium_org_third_party_angle,MSOpenTech/angle,bsergean/angle,ecoal95/angle,ppy/angle,ecoal95/angle,crezefire/angle,domokit/waterfall,csa7mdm/angle,jgcaaprom/android_external_chromium_org_third_party_angle,vvuk/angle,MIPS/external-chromium_org-third_party-angle,MIPS/external-chromium_org-third_party-angle,jgcaaprom/android_external_chromium_org_third_party_angle,vvuk/angle,mybios/angle,mrobinson/rust-angle,csa7mdm/angle,MSOpenTech/angle,mybios/angle,android-ia/platform_external_chromium_org_third_party_angle