Fail when *any* report file is empty

[timabell]

Describe

I had a test run with multiple report xml files, and one of them was empty. It took me a while to notice because the test run still passed, and the PR just collapsed eveything into a "checks passed" block.

Proposed solution

Fail the build / step

Research

I had a look at #220 which makes me think it's supposed to fail if there are no results (by default), so I'm guessing that the fact that one of xml files had a test result meant that was considered good enough.

Gratitude

Thanks for the great tool! Very much appreciated.