if MATOMO_SITE_ID is empty, don't add tracking code

There are some requests hitting anon-stats that look like: `action_name=CALL+this+is+a+test+call+%7C+EFF+Action+Center&idsite=&rec=1&url=http%3A%2F%2Flocalhost%3A3000%2Faction%2Fcall-this-is-a-test-call&urlref=` which result in errors because idsite parameter is empty.

Not sure exactly where these are coming from, but if we add some logic to not add the tracking code when idsite is empty, that might resolve the errors.