fix overflow check
I did some tests and unfortunately the test
```
pa_array.nbytes > MAX_BATCH_BYTES
```
doesn't work. Indeed for a StructArray, `nbytes` can be less 2GB even if there is an overflow (it loops...).

I don't think we can do a proper overflow test for the limit of 2GB...

For now I replaced it with a sanity check on the first element.