Only add image data to the dimension 3 source.
Images are all we render, and only from block 0.
@dcthomp this fixes a bug where the volume slices weren't displayed after a resource with both .med and images was saved and reloaded.
Images are all we render, and only from block 0.
@dcthomp this fixes a bug where the volume slices weren't displayed after a resource with both .med and images was saved and reloaded.