Incorrect warning when replacing unpublished, ingested .xlsx

[adam3smith]

Not a major error or problem, but unexpected behavior, and I'd argue a minor bug:

Steps to reproduce on demo.dataverse.org with v. 5.4.1 build 430-80361bf:

1. Upload an .xslx file to a dataset
2. Wait for the file to ingest -- the file is now listed as filename.tab
3. Use the "Replace" option from the File Options menu and select a different .xlsx file type
4. Dataverse displays a warning that you're trying to replace a file with another file of a different type -- but that's not actually the case: the original file is .xlsx in both cases