Produce report, even if no CI builds are found

[aDotInTheVoid]

Currently, if their are no ci builds, a report isn't printed as here an error is returned

cargo-bisect-rustc/src/main.rs

Lines 1146 to 1152 in 37e4366

	if commits.is_empty() {
	bail!(
	"no CI builds available between {} and {} within last 167 days",
	start,
	end
	);
	}

so this function exits early

cargo-bisect-rustc/src/main.rs

Lines 615 to 619 in 37e4366

	let ci_bisection_result =
	bisect_ci_via(cfg, client, &*cfg.repo_access, &working_commit, &bad_commit)?;
	print_results(cfg, client, &ci_bisection_result);
	print_final_report(cfg, &nightly_bisection_result, &ci_bisection_result);

It would be nice to show a report, even if their are no CI builds availible

[savente93]

Am having a look at this. Would it be acceptable to just print the results that are there or is more work needed? (i.e. if there is no CI builds available, just print the nightly bisection report and not the rest)