Fix #143775: Cryptomatte: Precision issues with matte output

The issue has been introduced in 7ceb4495c5 by missing implementation
of the is_noop() callback for the CPU processor.

While it was not noticeable perceptually, an exact floating point value
might have changed due to un-premultiplication+premultiplication.

The fix needs to be ported to the Blender 4.5 LTS.

Pull Request: https://projects.blender.org/blender/blender/pulls/143998

source/blender/imbuf/opencolorio/intern/libocio/libocio_cpu_processor.hh

@@ -22,7 +22,7 @@ class LibOCIOCPUProcessor : public CPUProcessor {
 
   bool is_noop() const override
   {
-    return false;
+    return ocio_cpu_processor_->isNoOp();
   }
 
   void apply_rgb(float rgb[3]) const override;