Fix list builder bug. See #5, #7

Thanks! Also, did you notice that you won the lottery? Pipeline number 10000!

merged

mentioned in commit b14a3932

FYI: Somewhat unfortunately, PyOpenCL has two issue trackers:

• https://github.com/inducer/pyopencl/issues
• https://gitlab.tiker.net/inducer/pyopencl/issues

To keep things unambiguous, it's better to add "#5 (closed) on gitlab" or some such.