Sorry, been away from the pc.
You can run the command as is straight as a sensor in HASS (just using the curl command as your “command:”), but this reduces your ability to troubleshoot. (You can change the mediachecker.sh script without needing to restart HASS).
Check that the IP for Kodi is correct, and make sure you have the remote control api turned on (in your Kodi interface, go to System/Settings/Network/Services, activate Allow control of Kodi via HTTP). You can check the port from there, as well. If you are running the http interface on a port other than 80, you will need to add it to the curl command. (Like Bit-River did with :8080).
Let me know if that helps