read_array_of_* with 0 elements fails when memory is not accessible

```
[1] pry(main)> p
=> #<FFI::Pointer address=0x00000000000000>
[2] pry(main)> p.read_array_of_long(0)
FFI::NullPointerError: invalid memory read at address=0x00000000000000
from (pry):2:in `read_array_of_long'
```

I am expecting no memory reads when reading an array of length 0, so this should just return an empty array.
