When multiple F-Curves have the `FCURVE_ACTIVE` flag set, only one of them
was drawn in the graph editor.
Only one F-Curve should be marked with this flag, but that's not something
the datamodel enforces. Because of that, it apparently is possible to get
into a situation where multiple F-Curves are marked as such. They are now
all drawn properly.
Pull Request: https://projects.blender.org/blender/blender/pulls/137102
06231cc8b3