CMCL-1594: missing null check in deoccluder

[glabute]

Purpose of this PR

CMCL-1594: missing null check generated console exceptions.

Testing status

• Added an automated test
• Passed all automated tests
• Manually tested

Documentation status

• Updated CHANGELOG
• Updated README (if applicable)
• Commented all public classes, properties, and methods
• Updated user documentation

Technical risk

none whatsoever

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 26.83%. Comparing base (d565c83) to head (be2e2ee).
Report is 1 commits behind head on main.

Files	Patch %	Lines
...achine/Runtime/Behaviours/CinemachineDeoccluder.cs	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1001   +/-   ##
=======================================
  Coverage   26.83%   26.83%           
=======================================
  Files         249      249           
  Lines       27999    27999           
=======================================
  Hits         7513     7513           
  Misses      20486    20486           

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