Dear all,

we hit a NULL pointer dereference when trying to simplify PACK
when the MASK argument was present.  The obvious and trivial
solution is to check for NULL pointer dereferences why looking
at the constructor for the ARRAY argument, which we already do
in the case the MASK is not present.

Committed to mainline after regtesting on x86_64-pc-linux-gnu
as commit r13-2691-g2b75d5f533b9d6b39f4055949aff64ed0d22dd24

This is a 10/11/12/13 regression, so I will check if it can
be backported.

Thanks,
Harald