fix: ignore if we have dhparam.pem file already
There is case when the file can already exists. The idea was to not overwrite it but it is possible that it is left after us. Failing to run this fix results in OpenVPN server being broken.
Should fix turris/foris-controller/foris-controller-openvpn-module#25 (closed)
Companion MR build!421 (merged)
Edited by Karel Koci