Fix EZP-23390: Legacy IO loads whole file to get mime type with FS clust...

...er handler

Todo:
- [ ] Get [legacy PR](https://github.com/ezsystems/ezpublish-legacy/pull/1082) merged and change composer.json to reflect that before merging this
Is there any chance that this method will be called for an `images-versioned` URI (e.g. an archived or unpublished image created by the legacy kernel) ?