BUG: fix write/read roundtrips with empty Table dumped to ECSV #15515

Job	Run time
Mandatory checks before CI	8s
allowed_failures / Load tox environments	4s
tests / Load tox environments	9s
allowed_failures / (Allowed Failure) Python 3.12 with remote data and dev version of key dependencies	11m 59s
allowed_failures / (Allowed Failure) Python 3.11 with dev version of matplotlib	7m 20s
tests / Python 3.11 with minimal dependencies and full coverage	9m 58s
tests / Python 3.10 in Parallel with all optional dependencies	7m 37s
tests / Python 3.9 with oldest supported version of all dependencies	14m 7s
tests / Python 3.10 with all optional dependencies (Windows)	11m 0s
tests / Python 3.10 with all optional dependencies (MacOS X)	18m 41s
tests / Python 3.9 Double test (Run tests twice)	12m 34s
	1h 33m 37s

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