In the schedule phase (and only in this phase!) the node 0 was not
being selected due to `!0` being true. We meant to be checking
against undefined rather than this.

Bug: v8:7327
Notry: true
Change-Id: Ie675979219868725b0e345065cec7a2a7091fda8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3008215Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75585}