Emitting acceptor errors terminates the really slow search for licenses

`cargo about generate` stops looking for licenses after it finds a license which was not accepted. This is especially annoying when working with many files as the current iteration approach is really quite slow.

For comparison. [ripgrep](https://docs.rs/ripgrep) even with `--no-ignore` flies through all my files almost immediately. It would be worth taking a few pages out of rg's book.

**Edit**: [cargo license](https://docs.rs/cargo-license) does not do the deep analysis to find licenses but is immediate to give feedback.

Start at the `cargo about generate` entry point and reproduce the slow search with many files, including a license that is not accepted. Trace how an acceptor error ends the search and compare the traversal behavior with ripgrep; done means rejected licenses no longer terminate discovery and the search gives substantially faster feedback.

Written by the indexing model from the issue text.