Refactor to use while-let in buffer.integrate_edit()

[MoritzKn]

This really is a minor refactor but I came a cross it while looking through the code and thought I may as well just submit it.

What Refactor to use while-let syntax instead of a manuell check and assignment

Why

• Replaces two item() calls with just one
• Gets rid of an .unwrap() call
• More idiomatic code

[nathansobo]

Thanks!