resurrect is_unsigned_iterator

cpp/include/cudf/detail/gather.cuh

@@ -83,7 +83,8 @@ struct gather_bitmask_functor {
     auto col     = input.column(mask_idx);
 
     if (Op != gather_bitmask_op::DONT_CHECK) {
-      bool out_of_range = (row_idx < 0 || row_idx >= col.size());
+      bool out_of_range = is_signed_iterator<MapIterator>() ? (row_idx < 0 || row_idx >= col.size())
+                                                            : row_idx >= col.size();
       if (out_of_range) {
         if (Op == gather_bitmask_op::PASSTHROUGH) {
           return bit_is_set(masks[mask_idx], bit_idx);

cpp/include/cudf/utilities/traits.hpp

@@ -224,6 +224,18 @@ constexpr inline bool is_unsigned(data_type type)
   return cudf::type_dispatcher(type, is_unsigned_impl{});
 }
 
+/**
+ * @brief Indicates whether the `Iterator` value type is unsigned.
+ *
+ * @tparam Iterator  The type to verify
+ * @return true if the iterator's value type is unsigned
+ */
+template <typename Iterator>
+constexpr inline bool is_signed_iterator()
+{
+  return std::is_signed<typename std::iterator_traits<Iterator>::value_type>::value;
+}
+
 /**
  * @brief Indicates whether the type `T` is a floating point type.
  *