Nuke: Nuke Slate MXF review fails on 23.976 FPS project

[jrsndl]

Describe the bug
DNxHD MFX has strict specifications. When generating one frame MXF for slate 23.976 project, ffmpeg needs fps expressed as 24000/1001.

To Reproduce

1. Create 23.976 project with MXF review
2. Go to Nuke, add Nuke Slate, publish
3. Publish fails on creating one frame MXF
4. See error:

[mxf_opatom @ 00000257f5154100] Unsupported frame rate 1199/50. Set -strict option to 'unofficial' or lower in order to allow it! 
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument 
Error initializing output stream 0:0 --  
Conversion failed! 

Additional context
Allowing 23.98 (1199/50) might not allow succesful concatenation with the review file.
Possible fix: FFprobe can read the framerate in 24000/1001 form: r_frame_rate.

[cuID:25u4edx]