fix: fix potential underflow

Co-authored-by: Michael Davis <mcarsondavis@gmail.com>

helix-term/src/ui/completion.rs

@@ -93,7 +93,7 @@ impl menu::Item for CompletionItem {
                             }) => value,
                         };
                         // LSPs which send Color completion items include a 6 digit hex code at the end for the color. The extra 1 digit is for the '#'
-                        text.get(text.len() - 7..)
+                        text.get(text.len().checked_sub(7)?..)
                     })
                     .and_then(Color::from_hex)
                     .map_or("color".into(), |color| {