Fixing the size getter leads to infinite loop.

Author: Xummer

swift/08_stack/StackBasedOnLinkedList.swift

@@ -14,8 +14,10 @@ struct StackBasedOnLinkedList<Element>: Stack {
 
     var size: Int {
         var count = 0
-        while head.next != nil {
+        var cur = head.next
+        while cur != nil {
             count += 1
+            cur = cur?.next
         }
         return count
     }