Was the marriage of Joseph and Mary sinful because it never produced children?

They were not married, so the premise does not hold. Joseph was betrothed to Mary, and that is where it stopped; there was no demand for them to have children. And Catholicism had not started yet; it would not begin until Jesus died, rose again, and inaugurated the new covenant. So whatever is required in Catholicism regarding marriage cannot be applied here. Your argument is anachronistic; you are combining two times that cannot be combined.