Add the KEY_END marker on key creation where missing

Add the KEY_END vararg where missing when creating a new key, either
using the C keyNew or the C++ kdb::Key, as done everywhere else.

This fixes crashes in some tests.
Hello, thank you, this is really wrong. We should add __attribute__ ((sentinel)) to get warnings on these, but then we also would have to fix keyNew(0, KEY_END) and ksNew(0, KS_END) and KEY_END would need to be a pointer.