feat: df.to_pandas_batches() returns one empty DataFrame if df is empty

[tswast]

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Fixes internal issue b/428918844
Towards internal issue b/428700094
Related to #1841 (comment)
🦕

[tswast]

e2e failures:

=========================== short test summary info ============================
FAILED tests/system/large/streaming/test_bigtable.py::test_streaming_df_to_bigtable
= 1 failed, 373 passed, 6 skipped, 6 xfailed, 6 xpassed, 238 warnings, 2 retried in 1490.68s (0:24:50) =

notebook failures:

------------------------------ Captured log call -------------------------------
ERROR    traitlets:client.py:568 Error occurred while starting new kernel client for kernel 6b697f25-7265-4473-944b-615ef14436e9: Kernel didn't respond in 60 seconds

Learn more about nbmake at [https://github.com/treebeardtech/nbmake](https://www.google.com/url?q=https://github.com/treebeardtech/nbmake&sa=D)

============================== slowest durations ===============================
61.19s call     notebooks/geo/geoseries.ipynb::geoseries.ipynb

(2 durations < 0.005s hidden.  Use -vv to show these durations.)
=========================== short test summary info ============================
FAILED notebooks/geo/geoseries.ipynb::geoseries.ipynb - NBMAKE INTERNAL ERROR
========================= 1 failed in 61.31s (0:01:01) =========================
Exception ignored in atexit callback: <bound method run_sync.<locals>.wrapped of <nbcl

Samples failures:

=========================== short test summary info ============================
FAILED classification_boosted_tree_model_test.py::test_boosted_tree_model - g...
============ 1 failed, 27 passed, 42 warnings in 2989.94s (0:49:49) ============

None of these appear to be related to the changes I've made in this PR.