When running `rustup update` and a component fails to download, already downloaded component are redownloaded on subsequent run.

[dzamlo]

Problem you are trying to solve

When running rustup update and a component fails to download, already downloaded component are redownloaded on subsequent run.

Step to reproduce:

1. Have multiple component to updates
2. Run rustup update
3. Have at least one component successfully download
4. Have a component failed to download, for example by disconnecting your internet connection
5. Rerun rustup update
6. The component that was successfully downloaded is downloaded again

Solution you'd like

When a component is downloaded and another component failed to download, the component that was successfully downloaded should not need to be redownloaded again.

This would be useful for person like me that have a bad internet connection and a lot of targets (and thus components) installed.

Notes

No response