Fixed an exception happening when the user doesn't set one of the renderers of a given LOD (case 1372965).

[anisunity]

https://fogbugz.unity3d.com/f/cases/1372965/
Before 2021.2 No LOD support, so no need for the fix.
After 2021.2, C++ culling, no need for the fix.

Testing status
Pair tested on the repro case with @remi-chapelain

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://unity-ci.cds.internal.unity3d.com/project/902/
Search for your PR branch using the search bar at the top, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

HDRP
/jobDefinition/.yamato%2Fall-hdrp.yml%23PR_HDRP_2021.2
With changes to HDRP packages, you should also run
/jobDefinition/.yamato%2Fall-lightmapping.yml%23PR_Lightmapping_2021.2

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.

[remi-chapelain]

Pair tested and already tested in this PR anyway !