[#1049] Don't truncate int64* and uint64* values returned from call-out; properly preallocate enough space, even on 32-bit architectures, for 64-bit integers when passing (u)int64* pointers to that space.

• Don't truncate int64* and uint64* values returned from call-out
• Preallocate enough space for 64-bit integers pointed to by int64* and uint64* (fix for 32-bit architectures)

This completes the fix for #1049 (closed) as !1441 (merged) only fixed (u)int64 not (u)int64*.