Add a test with an empty input range - should do nothing

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@305268 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/numerics/numeric.ops/transform.exclusive.scan/transform_exclusive_scan_iter_iter_iter_init_bop_uop.pass.cpp

@@ -122,6 +122,12 @@ void basic_tests()
         assert(v[i] == 40 + triangle(i));
     }
 
+    {
+    std::vector<int> v, res;
+    std::transform_exclusive_scan(v.begin(), v.end(), std::back_inserter(res), 40, std::plus<>(), identity<>());
+    assert(res.empty());
+    }
+
 //  Make sure that the calculations are done using the init typedef
     {
     std::vector<unsigned char> v(10);