BlendOutTime setting doesn't work when unlinking multiple anim layers

When we unlink the layer, we call UAnimInstance::PerformLinkedLayerOverlayOperation

In that function, ClassToSet is null, so we loop over the layer nodes and call SetLinkedLayerInstance(this, nullptr)

FAnimNode_LinkedAnimLayer::InitializeSelfLayer is then called for each layer, which:

• Gets the animbp class of the target anim instance so that RequestBlend can read its blend out settings
• Deletes the target anim instance

For any subsequent layers, the target anim instance is now deleted so we can't read the blend out settings.

• Create a layer interface with two layers
• Create an animbp that implements the interface, plays an animation in each layer, and sets the BlendOutTime to 2 seconds
• Create a main animbp that also implements the interface, but has a state machine with two states, and each state plays one of the layers
• Add an inertial blend node to the end of the main animbp
• Link the layer
• Unlink the layer

When the layer is unlinked, the pose will snap instead of blending for one of the layers.