[Bug]: DnsApp is deleted if manual update archive is malformed

[JCFruit]

Description

When manually updating DnsApp, if archive is malformed (for some reason), Technitium will throw an error (which is ok), but will also delete original version of DNS app with all it's configuration files.

If the same mechanism is used for automatic updates, theoretically it could mean that malformed app archive will delete apps for all users, possibly without them realizing it.

Reproduction steps

1. Manually add some app to server
2. Make archive server can't process, for example add password
3. Manually update app through UI
4. See error in UI and in logs
5. After returning to the app page, original app is gone

Log file

Screenshots

[JCFruit]

After investigating further, looks like it's a problem in ZipArchiveEntry.ExtractToFile with overwrite set to true.

It first opens destination file with FileMode.Create and only then tries to open ZipArchiveEntry. When ZipArchiveEntry.Open fails, original file is already replaced with zero-bytes version.