The struct wrappers generated by the FFI generate code where arrays of size 0 are allocated (?)

I have a guess at what the problem is and how to fix this, but I have not worked in this area of the compiler before. @sbs can you confirm this makes sense? Then I will implement the fix.

Bug

(From Stdlib Vector3f)

In the function SACf_Vector3f__wrap__struct_Vector3f__sa_S__sa_S__sa_S, we generate code that allocates an AKS of size 0:

    SAC_ND_ALLOC_BEGIN((SACp_emal_5145__ggtc_943, (AKS, (NHD, (NUQ, (INT, (GLO, (NON, (NOT, (OTH, ))))))))), 1, 1, SACarg *)

and the compiler rightfully complains that malloc(0) is implementation-defined behaviour. If it is intended that this array has size 0, we should set it to NULL.

Proposed fix

We can insert a check (SAC_ND_A_SIZE (var_NT) == NULL) as in the AKS case, the C-compiler knows statically that this is 0 and will optimize the check away.

I think this variable comes from generate_generic_type_conversions.c:

        /* Here, we build the standard variant:
         *
         *external
         * SACarg(---) <ns>::wrap_<name> (<ns>::<name>[*] arg);
         * #pragma linkname "SACARGwrap_<ns>__<name>"
         * #pragma linksign [1,2]
         */
        argtype = TYmakeAUD (TYcopyType (TYgetScalar (type)));
        rettype = TYmakeAKS (TYmakeSacargSimpleType (UT_NOT_DEFINED),
                             SHmakeShape (0));

which does suggest it is intended.