This fixes a crash that occured in the Lego trace when run with
an ES 3.0 context.
* At the end of each frame it unbinds all the image units using
glBindImageTexture, which is an ES 3.1 call.
* During validation, we verify things using ANGLE's internals,
but they are only set up when the context is >= ES 3.1.
* This led to a crash.
* The fix is to check the ES context early and bail, which
aligns with other entry points.
Test: LEGO MEC
Bug: b/161716126
Bug: angleproject:4048
Change-Id: I9aee2ee173436f5de5062758a70e0909f6fc9a7f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2462163Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Charlie Lao <cclao@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Cody Northrop <cnorthrop@google.com>
