C comment: fix for commit
b5a9b18cd0b
The commit was "Provide API for streaming relation data.".
Reported-by: Nazir Bilal Yavuz
Discussion: https://postgr.es/m/CAN55FZ3KsZ2faZs1sK5J0W+_8B3myB232CfLYGie4u4BBMwP3g@mail.gmail.com
Backpatch-through: master