Thumbnails don't use default font of user

[owochle]

Describe the bug
When having nerdfont terminals, the thumbnail does not use nerd fonts even when the default settings of the user is.

To Reproduce

1. Have a nerd font recording
2. choose a thumbnail with nerd characters in them
3. See error

Screenshots

Versions:

• asciinema server: latest (probably: v20240428)