Allow empty CURLOPT_CAINFO when there is a valid CURLOPT_CAPATH

[Alex Khouderchah via curl-library]

Hey all,

It seems like CURLOPT_CAINFO is always required to refer to a valid cert
file (when we're actually verifying certs), whereas CURLOPT_CAPATH is
allowed to be empty or refer to a non-existent directory. I'm unclear why
this asymmetry exists. Is there a reason why CURLOPT_CAINFO shouldn't be
allowed to be empty/invalid if CURLOPT_CAPATH is valid?

Thanks,
Alex