ID 370867 - The Viewer's downrez should not call proxy files from Read nodes

Problem summary
When using a Viewer's "Downrez" option, Read nodes will switch to their Proxy media, or an exception will be thrown if the Read node has an invalid Proxy file path.

Customer reported version:
Nuke 11.2v2

Customer reported platform:
Windows 10

Steps to reproduce:
1) Open Nuke and create a Read node in the Node Graph
2) In the Read node's Properties, set its proxy knob to an invalid file path, such as "abc123"
3) View the Read node, then set the Viewer' downrez knob to any value besides 1:1
4) Observe the following error message:

Alternative steps:
1) Download the attached fullres.exr and proxy.exr files.
2) Launch Nuke and create a Read node in the Node Graph, selecting the fullres.exr
3) In the Read node's Properties, set its proxy knob to the proxy.exr file
4) View the Read node, then set the Viewer' downrez knob to any value besides 1:1
5) Observe how the image in the Viewer has a blue tint, as the proxy file is being loaded even though Proxy mode is not enabled.

Expected behavior:
The Viewer's downrez should not utilize or depend on the proxy file.

Actual behavior:
Activating downrez will throw an exception if the proxy file location is invalid, or switch to using the proxy file if it exists.

Workaround:
Besides removing the proxy file from the Read node, there is no known workaround at this time.

Reproduced by Support in:
Nuke 16.0v4 - Windows 11
Nuke11.2v4 - Windows 7 - Mac10.13 - CentOS6.9
Nuke11.2v1 - Windows 7
Nuke11.1v4 - Windows 7
Nuke11.1v1 - Windows 7
Nuke11.0v4 - Windows 7
Nuke11.0v1 - Windows 7
Nuke10.5v7 - Windows 7 - Mac10.13 - CentOS6.9
Nuke10.5v1 - Windows 7
Nuke10.0v6 - Windows 7
Nuke10.0v1 - Windows 7
Nuke9.0v9 - Windows 7
Nuke9.0v1 - Windows 7
Nuke8.0v7 - Windows 7
Nuke7.0v10 - Windows 7 - Mac10.13 - CentOS6.9

Earliest version tested
Nuke 7.0v10 - This issue appears to be in all versions of the product

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