style: fix clippy::redundant_guards lints

cordyceps/src/list.rs

@@ -365,7 +365,7 @@ impl<T: Linked<Links<T>> + ?Sized> List<T> {
         let split_idx = match at {
             // trying to split at the 0th index. we can just return the whole
             // list, leaving `self` empty.
-            at if at == 0 => return Some(mem::replace(self, Self::new())),
+            0 => return Some(mem::replace(self, Self::new())),
             // trying to split at the last index. the new list will be empty.
             at if at == len => return Some(Self::new()),
             // we cannot split at an index that is greater than the length of

util/src/io.rs

@@ -734,9 +734,7 @@ impl<T: BufRead, U: BufRead> BufRead for Chain<T, U> {
     fn fill_buf(&mut self) -> Result<&[u8]> {
         if !self.done_first {
             match self.first.fill_buf()? {
-                buf if buf.is_empty() => {
-                    self.done_first = true;
-                }
+                &[] => self.done_first = true,
                 buf => return Ok(buf),
             }
         }