Fix scanning when no commits are found

[cornelius]

No description provided.

[mxmehl]

I'm not sure whether this still is a problem after the changes done in #11:

contribution-checker/contribution_checker/_commits.py

Lines 173 to 185 in 24369a5

	def analyse_dates(report: RepoReport) -> None:
	"""Do some analysis of the dates of matched commits"""
	if report.matched_commit_data:
	report.matched_total = len(report.matched_commit_data)
	report.matched_oldest = min(report.matched_commit_data)
	report.matched_newest = max(report.matched_commit_data)
	else:
	logging.warning(
	"No commits found for %s. Either there was no match for your search, "
	"or the repository is broken in the cache or during clone. "
	"You may run with --debug/--verbose and check earlier errors.",
	report.path,
	)