CSM shadow casters falsely culled due to incorrect primitive octree test

While setting up whole scene shadows, CasterOuterFrustum is used to cull shadow casters from PrimitiveOctree. CasterOuterFrustum doesn't extend far back enough, which means that if an octree node fits tightly around a primitive, it's possible the octree node fails the intersection test and therefore gets culled incorrectly. This causes missing shadow casters behind the camera, even when they are in the CSM range.

• In code, on Engine\Source\Runtime\Renderer\Public\PrimitiveSceneInfo.h line 831, change MaxElementsPerLeaf = 256 to MaxElementsPerLeaf = 1. This will make it easier to setup a scene where the octree fits tightly around the primitives in the next steps. You can use "r.shadow.visualizeprimitivetree 1" to show the nodes of the primitivetree.
• Make sure VSMs are disabled.
• Create a blank scene.
• Create a cube at (X=-3500.000000,Y=-1500.000000,Z=4500.000000)
• Create a sphere at (X=-3500.000000,Y=-500.000000,Z=4500.000000)
• Add a plane at 0,0,0 to receive shadows from the previously created primitives.
• Add a directional light. Make sure it casts shadows correctly onto the plane.
• Move the camera between the shadow casters and receiver. Notice how when the cube shadow first disappears, hiding the sphere makes it show up again.