WebGPU: Finalize command blocks when starting a new one The command buffer abstraction would not finalize blocks of commands when creating a new block, leading to possible infinite loops when processing the commands. Bug: chromium:413078308 Change-Id: Idf4e95a5ccc71f3ddc9a4202e5e000c0e2cd5f87 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6629473 Reviewed-by: Liza Burakova <liza@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>