void clear() {
		if (activeFile != null) {
			throw new AssertException("Snapshot already in progress");
		}
		snapshotFiles[0].delete();
		snapshotFiles[1].delete();
		changeFiles[0].delete();
		changeFiles[1].delete();
	}
Returns the recovery change data file for reading or null if one is not available.
The caller must dispose of the returned file before peforming generating any new
recovery snapshots.
@throws IOException
Ghidra/Framework/DB/src/main/java/db/buffers/RecoveryMgr.java