VirtualBaseTable createVirtualBaseTable(Address address) {
		VirtualBaseTable vbt = vbtByAddress.get(address);
		if (vbt != null) {
			String message =
				"PDB: warning virtual base table already exists for address: " + address;
			PdbLog.message(message);
			Msg.info(this, message);
		}
		else {
			vbt = new VirtualBaseTable();
			vbtByAddress.put(address, vbt);
		}
		return vbt;
	}
Returns the offset from the virtual base table entry
@param address Address of virtual base table
@param ordinal index into table
@return the offset
@throws PdbException if no table exists for address or no entry exists for ordinal
Ghidra/Features/PDB/src/main/java/ghidra/app/util/pdb/pdbapplicator/VbtManager.java