"Source should be ready" when running on a crate that uses a private registry

[qrnch-jan]

I recently set up margo and a simple Rocket server to host a private crate registry. The web server is configured to require basic authentication, and cargo is configured with the appropriate authentication information in ~/.cargo/config.toml (in the sense that I can add/use dependencies from the private registry).

When I run cargo outdated on a crate that has a dependency in my private registry, cargo outdated terminates relatively quickly with a panic:

$ cargo outdated --depth=1
    Updating `qrnch-priv-reg` index
thread 'main' panicked at /Users/jan/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-outdated-0.15.0/src/cargo_ops/temp_project.rs:404:18:
Source should be ready
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[qrnch-jan]

Duplicate of #366