Some values (not properly handled by do_versions?) could cause
'rna_backup_restore()' to throw an error resulting in the whole preview
generation not being saved to the .blend file.
I've checked folowwing demo files:
Here the offending seetings were:
- UnitSettings (length_unit, ...)
- FFmpegSettings (ffmpeg_preset, ...)
For now, these are now excluded in exclude_props