to the left of the actual bool value.  While in most cases there won't be
any, our support for old-style user-defined functions violates the C spec
to the extent of calling functions that might return char or short through
a function pointer declared to return "char *", which we then coerce to
Datum.  It is not surprising that the result might contain garbage
high-order bits ... what is surprising is that we didn't see such cases
long ago.  Per report from Magnus.