When not finding a host in ~/.ssh/known_hosts, the return value is 0 if the host just is not found. We then never check the system host file in /etc. This fixes the code to check /etc on any failure, not just a bad return code.
Merge pull request #5695 from kormoc/fix_git_check_hostkey_2

Fix case where there is a ~/.ssh/known_hosts file and the host key is only in /etc/ssh/ssh_known_hosts