Mirax files always have adjacent files.
Mirax files always have adjacent files.

This always uses the fuse path to access mrxs files if possible, as mrxs
files always have adjacent files.  Fixes
https://github.com/DigitalSlideArchive/HistomicsTK/issues/579.

DigitalSlideArchive/large_image,DigitalSlideArchive/large_image,girder/large_image,DigitalSlideArchive/large_image,girder/large_image,girder/large_image