k_smallest(0) and variants: consume the iterator

The iterator can have side effects so I think it should be consumed in all cases, even k=0.
If there are no side-effect then maybe the compiler will optimize it away.

Author: Philippe-Cholet

src/k_smallest.rs

@@ -42,6 +42,7 @@ where
     }
 
     if k == 0 {
+        iter.last();
         return Vec::new();
     }
     let mut iter = iter.fuse();

src/lib.rs

@@ -2972,6 +2972,7 @@ pub trait Itertools: Iterator {
         use alloc::collections::BinaryHeap;
 
         if k == 0 {
+            self.last();
             return Vec::new().into_iter();
         }