DatumGetPointer() takes a Datum argument, not a pointer.
This is cosmetic given the current definitions of the
underlying macros, but it's still formally a type violation.

Bug was introduced in commit 389bb281, but there seems
no need to back-patch.

Dagfinn Ilmari Mannsåker

Discussion: https://postgr.es/m/d8jlfsxq3a0.fsf@dalvik.ping.uio.no