Fix IMagick with s3 compat

In some cases (it's not that clear how) Imagick is not compatible with remote streams. According to the docs, this has never been possible, but I think it happened to work in the past. I've tried the same version of imagick, on different sets and sometimes works, some times doesnt. The crux of the issue is that IMagick tries to read from the stream, and is sending a SEEK request to something near PHP_MAX_INT, which causes memory allocation issues on our stream wrapper. It's maybe possible to work around it with a seek stream guard, but really I think that's just one of many possible issues. I think it's going to be better to let IMagick always work with local images to avoid issues.