Can't Add autorized_keys file for Support Module when .ssh dir doesn't exist

It appears that the support module isn't able to add the authorized_keys file when the /root/.ssh doesn't already exist (seen in request #4792):

Adding Virtualmin SSH keys to /root/.ssh/authorized_keys ..
Failed to enable remote login : Failed to open /root/.ssh/authorized_keys for writing : Bad file descriptor

I verified that on the system in question, the .ssh dir does not yet exist.