Rectify bug in initialization of offsets for uniform variables Make sure to set a uniform's flattenedOffsetInParentArrays value only if it has a valid parent array index. Serialize/Deserialize flattenedOffsetInParentArrays value. Bug: angleproject:3216 Bug: angleproject:3217 Bug: angleproject:3665 Change-Id: I6e4d003b1dd74b330bcf153f8d3df92414f198dd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1704219 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>