ID 472519 - The CopyCat node errors when training with multichannel files.

Problem summary
The CopyCat node errors when training with multichannel files.

Customer reported version
nuke.13.0v1

Customer reported platform
n_a_linux

Steps to reproduce

1) In Nuke, read in two multi-channel exr files.

2) Create a CopyCat node and add the .exr files as GroundTruth and Input.

3) Select the start training button on the CopyCat node.

Expected behavior
The CopyCat node should complete the training with multiple channels present.

Actual behavior
The node errors out after caching the inputs with a message prompt: "CopyCat1: Exception while executing"

Workaround
Using a Shuffle or Remove node to maintain a single channel works without issue.

Reproduced by Support in:
Nuke 13.0v1 - Windows 10, CentOS 7, macOS 10.14

Unable to reproduce bug in:
Nuke 12.2v5 - Windows 10, CentOS 7, macOS 10.14

Earliest version tested
Nuke 12.2v5 - This feature did not exist before this version