private void init(boolean atStart) {
        if (pm.hasProperty(current)) {
			if (atStart) {
	            doesHaveNext = true;
			}
			else {
				doesHavePrevious = true;
			}
        }
    }
checks to see if the start index has a property so that the first
call to next() will return that index.
Ghidra/Framework/Generic/src/main/java/ghidra/util/map/LongIteratorImpl.java