This changes the `action.frame_range` Python API to return an accurate
frame range for actions. Specifically, it was previously special-cased
to return a range with length 1 whenever the length was actually 0. This
led to a bizarre situation where a real frame range of `[0.0, 0.2]` would
return that range as-is, but a real frame range of `[0.0, 0.0]` would
instead return a range of `[0.0, 1.0]`.
The new behavior simply always returns the real frame range.
The reason for the previous behavior was obscure: the relevant code was
also used internally in Blender's NLA system, and returning a zero-length
range could result in NLA strips getting infinite scale. The code is now
separated out appropriately so that the NLA system still gets the
non-zero-length range, while the Python API for actions returns the real
range.
Pull Request: https://projects.blender.org/blender/blender/pulls/112709
49eab72141