If a uniform location is unused, but a call to glBindUniformLocation has
explicitly bound the uniform, ANGLE validation still treated the uniform
as unused and returned errors. The correct behavior is to ignore the
uniform and silently fail.

Bug: angleproject:4374
Change-Id: Ic7b97f23cf8bc2d5380129322595e51b3d4a9fcc
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2036676
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>