Refactor header appending logic for better readability

[dukbong]

This PR refactors the logic for adding headers in the appendXForwarded and appendForwarded methods.

Additionally upon reviewing both the original and refactored code, I noticed that in appendXForwarded, the result of headers.getFirst() is only checked for null. Wouldn't it be better to use StringUtils.hasText() instead, to ensure not only that the value is non-null but also that it contains text? What do you think about this approach?