The command in your sudoers file is:
/usr/bin/systemctl stop vdr.service
but, at the command line, you are attempting to execute:
/usr/bin/systemctl stop vdr
A solution: Add both variations to your sudoers file:
martin ALL=(ALL) NOPASSWD: /usr/bin/systemctl stop vdr
martin ALL=(ALL) NOPASSWD: /usr/bin/systemctl stop vdr.service
BTW, a good practice it to place custom sudoders rules into files created in /etc/sudoers.d directory. Such a file can be created with one of the following commands:
sudo visudo -f /etc/sudoers.d/martin-vdr-service
sudo visudo /etc/sudoers.d/martin-vdr-service # [1]
[1] “As of version 1.8.27, the sudoers path can be specified without using the -f option.” – man page for visudo