My main goal (for this entire MR) is to shut up that MESSAGE for Z:. Judging by commit 4907f262, the goal is to print that only if the device is a mounted ISO file or an actual optical drive. Let's check for specifically that.
It certainly doesn't worth to do a lot of things to get rid of a message in the log. I personally doubt shutting it up is too much useful, but maybe that is just me. If this has to be done it is better not to build up heuristics about that but rather make it a FIXME (so it doesn't show up with WINEDEBUG=-all), or WARN or remove it. But anything without building the whole framework around that or otherwise complicating things. But note that the output is needed for debugging only, the best and only sane way to make it silent is to redirect stderr to /dev/null.