Crash when hovering a filtered-out part in an active tab view timeline

STR:

1. open https://main--perf-html.netlify.app/public/340vdp6yxpznvhsepjf04sez4f75csz5fw5eg78/stack-chart/?range=3615m984~3655m182&resources&thread=i&v=8&view=active-tab
1. hover the small greyed-out part near the right of the panel.

Strangely, this part disappears after zooming in. Also it doesn't appear in the stack chart. Then my guess is that it's a bug in the activity graph.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-590)