private T getSelectedOpenDomainObject() {
		if (!usingOpenProgramList()) {
			return null;
		}
		return openObjectsTable.getSelectedRowObject();
	}
Return the selected version number from the history panel.
@return -1 if a version history was not selected
Ghidra/Features/Base/src/main/java/ghidra/framework/main/OpenVersionedFileDialog.java