[libc++][ranges] check the precondition in '__shift_left'

Author: xiaoyang-sde

libcxx/include/__algorithm/shift_left.h

@@ -29,6 +29,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 template <class _AlgPolicy, class _Iter, class _Sent>
 _LIBCPP_HIDE_FROM_ABI constexpr pair<_Iter, _Iter>
 __shift_left(_Iter __first, _Sent __last, typename _IterOps<_AlgPolicy>::template __difference_type<_Iter> __n) {
+  _LIBCPP_ASSERT_UNCATEGORIZED(__n >= 0, "__n must be greater than or equal to 0");
+
   if (__n == 0) {
     _Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
     return {std::move(__first), std::move(__end)};