Add regression test for ArrowWriter.write_batch when batch is empty (huggingface#4510)

* Fix if-statement logic in `write_batch`

* Add regression test on `test_write_batch`

* Replace AND-condition with OR in `write_batch`

* Remove `write_batch({})` in `test_write_batch`

* Add valid batch as `write_batch` arg

* Revert if-statement change in `write_batch`

Author: Álvaro Bartolomé

tests/test_arrow_writer.py

@@ -179,6 +179,7 @@ def test_write_batch(fields, writer_batch_size):
     schema = pa.schema(fields) if fields else None
     with ArrowWriter(stream=output, schema=schema, writer_batch_size=writer_batch_size) as writer:
         writer.write_batch({"col_1": ["foo", "bar"], "col_2": [1, 2]})
+        writer.write_batch({"col_1": [], "col_2": []})
         num_examples, num_bytes = writer.finalize()
     assert num_examples == 2
     assert num_bytes > 0