Add unit test for erroneous empty rfile

[ddanielr]

Is your feature request related to a problem? Please describe.
Add a Unit test for checking a valid rfile index entry that points to a datablock that is expected to be non-empty, but returns no data for the block.

Ideally this should throw an exception and interrupt any actions that were dependent on the datablock contents.

[ddanielr]

This ticket is a sub-task for #3694

[ctubbsii]

@keith-turner suggested possibly using our own test FileSystem implementation that throws exceptions as well.