When emulating streamed attributes, the internal state is not
being correctly updated in the GL backend.
This fixes this issue for the particular edge-case.

Bug: angleproject:3933
Change-Id: I4b785d76ccfc475d80e431977e4d482c7f2d1389
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1817103Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>