When running the reference viewer with multiple assets, the Show Referenced/Referencing Objects command only shows references for the first asset selected

Though we allow multiple assets to be selected when starting the reference viewer and generate the tree for the combined asset group, we don't take the other assets into account when generating the list of referenced or referencing assets. Those lists should be consistent with what we see on the graph.

1. Select two or more assets in the content browser
2. Right click and select Reference Viewer
3. Right click the combined node for your assets and select "Show Referenced Objects List"
4. List will only contain referenced objects for the first asset you selected