Clicking in a blank part of the activity graph re-selects the selected node

Profile: https://share.firefox.dev/3D0sJvr

Steps to reproduce:

1. Click somewhere in the green parts of the Renderer thread's activity graph. This selects a row in the tree view.
1. Scroll the tree view so that the selected row is out-of-view.
1. Click somewhere in the blank parts of the Renderer thread's activity graph, e.g. in the parts with 0% CPU.

Expected results:
Probably nothing should happen. The selection shouldn't change and the tree shouldn't scroll.

Actual results:
The selection remains unchanged, but the selected row is scrolled back into view.

The same happens in the stack chart and flame graph.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-444)