caddy-frontend: Avoid needless double slashing for type:zope

For case if path (for zope) is provided from
/VirtualHostBase/https//example.com:443/zope_path/VirtualHostRoot/url_path
to
/VirtualHostBase/https/example.com:443/zope_path/VirtualHostRoot/url_path

If path (for zope) is not provided from

/VirtualHostBase/http//example.com:443//VirtualHostRoot/url_path
to
/VirtualHostBase/http/example.com:443/VirtualHostRoot/url_path