This will fail for any binary file.  I think we shouldn't merge this until we can either consistently disable the menu item for binary files (though even that would feel a little weird), or ideally add a shell API that lets this work for binary content.

I believe @couzteau has been looking into making FileSystem support binary file IO, so that's one option (he's on vacation until after the holidays, though).  Another option would be to add a simpler brackets-shell API that invokes the standard OS file-copy API, without needing us to read & rewrite the file at all.  That seems like the ideal solution, since it would be faster and would do a better job of preserving metadata.