DataBuffer getOldBuffer(DataBuffer buf, int index) throws IOException {
		if (versionFile == null) {
			throw new IOException("Version file is closed");
		}
		int vfIndex;
		try {
			vfIndex = bufferIndexMap.get(index);
		} catch (NoValueException e) {
			return null;
		}
		versionFile.get(buf, vfIndex);
		return buf;
	}
Get original buffer associated with the specified storage index in the 
original file.
@param buf data buffer
@param index storage index
@return data buffer or null if buffer has not been modified
@throws IOException if an IO error occurs
Ghidra/Framework/DB/src/main/java/db/buffers/VersionFile.java