private void advanceToken() {
		if (currentToken == null) {
			return;
		}
		indexStack[depth] += direction;
		normalize();
	}
Update the node stack so that it points to the next ClangToken.  The next token is either
the predecessor or the successor depending on the direction setting (-1 or 1) respectively.
currentToken is set to the next token.  If there is no next token, currentToken is set to null.
Ghidra/Features/Decompiler/src/main/java/ghidra/app/decompiler/TokenIterator.java