public char previous() {
		try {
			return string.charAt(--index);
		}
		catch (IndexOutOfBoundsException e) {
			index = 0;
			return DONE;
		}
	}
Decrements the current index by one and returns the character
at the new index. If the current index is 0, the index
remains at 0 and a value of DONE is returned.
@return the character at the new position or DONE
Ghidra/Features/Base/src/main/java/ghidra/app/util/demangler/CharacterIterator.java