Profiler crash when clicking frame in marker stack

[mstange]

Steps to reproduce:

1. Open this profile
2. Click on one of the first SetNeedsStyleFlush markers
3. Click on the initPage frame in the marker stack in the tooltip.

Expected results:

The bottom box should open.

Actual results:

Uh oh, some unknown error happened in profiler.firefox.com.
TypeError: can't access property "libIndex", e is undefined.

┆Issue is synchronized with this Jira Task