primitives.

With the introduction of coding tables for boring types inside FIDL tables
to support linearization, array coding tables may have a null element,
when the array is in a FIDL table but the element is a boring type.

TEST: fx run-host-tests fidl_cpp_unittests
Change-Id: I56380c36369e4b501f5b82aa9cfc673c564f82a1