Handle erroneously empty rfile block reads

**Describe the bug**
When HDFS returns empty results for a rfile block that actually has data, Accumulo does not error or attempt additional validation of the rfile block. This can cause issues with metadata table reads as specific tablet contents fail to return.

**Versions (OS, Maven, Java, and others, as appropriate):**
- Affected version(s) of this project: 1.10.3

**Expected behavior**
Accumulo should be able to determine if a rfile content location is actually empty or if data should have been returned.