[system-analyzer] Fix zoom

Don't render if the timeline track doesn't have any data.

Change-Id: Ib0638ce18391f14212d3a5385d90877cf0392c5f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3162042


Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76843}