Fix broken commit r258888. I missed adding two pointer conversions

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@258893 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/forward_list b/include/forward_list
index a324fc3..78bcc55 100644
--- a/include/forward_list
+++ b/include/forward_list
@@ -326,7 +326,7 @@
     _LIBCPP_INLINE_VISIBILITY
     __forward_list_iterator& operator++()
     {
-        __ptr_ = __ptr_->__next_;
+        __ptr_ = __traits::__as_iter_node(__ptr_->__next_);
         return *this;
     }
     _LIBCPP_INLINE_VISIBILITY
@@ -410,7 +410,7 @@
     _LIBCPP_INLINE_VISIBILITY
     __forward_list_const_iterator& operator++()
     {
-        __ptr_ = __ptr_->__next_;
+        __ptr_ = __traits::__as_iter_node(__ptr_->__next_);
         return *this;
     }
     _LIBCPP_INLINE_VISIBILITY