Delete the whole linked list (omg noob?).

lib/stack.c

@@ -29,10 +29,16 @@ void initialize_stack(struct stack *stack) {
 }
 
 void delete_stack(struct stack *stack) {
+  struct stack *tmp_stack;
+
   if (stack) {
+    while (stack) {
+      tmp_stack = stack->next;
       delete_card(stack->card);
-  }
       free(stack);
+      stack = tmp_stack;
+    }
+  }
 
   return;
 }