RWP doesn't handle name conflicts in uploaded files well

[tw4l]

trafficstars

What's happening

If I upload a WACZ or WARC file to replayweb.page that has the identical name of an existing uploaded file (e.g. screenshots.warc.gz), I am taken to the older/already uploaded content without a warning. This led me to believe I was looking at my newly uploaded file when I in fact wasn't.

What I'd expect

Either:

1. Show an error message indicating what's happened/prevent upload; don't take me to different content

or ideally...

2. Handle the name conflict gracefully and make sure that the user is taken to the correct (newly uploaded) content