implement nth_back for Bytes

Author: koalatux

src/libcore/str/mod.rs

@@ -795,6 +795,11 @@ impl DoubleEndedIterator for Bytes<'_> {
         self.0.next_back()
     }
 
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        self.0.nth_back(n)
+    }
+
     #[inline]
     fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
         P: FnMut(&Self::Item) -> bool