Cross-browser compatibility fix for File.Select.file(s) in elm/file

I haven’t had a chance to set up the HTML gists, but I tested the variants you supplied here by swapping them into my application, and the last one (the one that doesn’t append the node but keeps it outside of the scope of the function), seems to work on all of my devices (Chrome on Android 8, Safari on iOS 10, Chrome/Firefox on Linux).

This looks very promising!