`ActionSlot::idtype` needs some extra care when reading from a blend
file. Blender's generic endian switching needs to be un-done, as the
ID type values are not numerically the same between little and big
endian machines. Due to the way they are defined, they are always in
the same byte order, regardless of hardware/platform endianness.
This is the same for Action Slots as #128129 does for Actions, except
that Action Slots use a `int16_t` instead of `short` and thus don't
need a cast.
Pull Request: https://projects.blender.org/blender/blender/pulls/128438
a97fe64c4f