Fix Take::nth logic.

Author: Stebalien

src/libcore/iter.rs

@@ -2126,12 +2126,15 @@ impl<I> Iterator for Take<I> where I: Iterator{
 
     #[inline]
     fn nth(&mut self, n: usize) -> Option<I::Item> {
-        if self.n == 0 {
-            None
-        } else {
-            let n = cmp::min(self.n-1, n);
+        if self.n > n {
             self.n -= n + 1;
             self.iter.nth(n)
+        } else {
+            if self.n > 0 {
+                self.iter.nth(self.n - 1);
+                self.n = 0;
+            }
+            None
         }
     }