unhelpful error for defective images

[FND]

Trying to convert a bunch of JPGs resulted in

node:internal/process/promises:289
            triggerUncaughtException(err, true /* fromPromise */);
            ^
[Error: Input file contains unsupported image format]

That's not particularly helpful. Turns out one of those images is defective, so we're missing a catch here for unexpected errors. We'd mostly need to annotate the respective file name for diagnosis, but I didn't want to discard more specific errors from within the respective function. I guess we should start using error codes or custom error classes?