REGR: follow-up to return copy with df.interpolate on empty DataFrame
follow-up to #35543
do we want to test this explicitly in this case > do we want to test this explicitly in this case

sure could add a test @jreback OK to merge (and backport) thanks. I still don't tihink this is actually the correct place to do this (as it should be handled gracefully in the internal interpolate), but not a blocker. @meeseeksdev backport 1.1.x