response: fix RES_LINE body data handling - v2

[cccs-sadugas]

See #362 for previous version.

Changes since last version

• Test the data in each callback call separately.

Testing/QA

I ran make check to make sure existing tests still pass.

The callback gets called once too many when running under valgrind. This is odd but some other tests also fail under valgrind on 0.5.x.

[cccs-sadugas]

@catenacyber ready for another review.

[catenacyber]

Thanks @cccs-sadugas for spotting and fixing this

[victorjulien]

Merged in #365, thanks!