ooo: "sniff" the full CSV file to guess delimiter

When sniffing only the first 1024 bytes, sometimes csv module is not able to determine delimiter, as reproduced with the added test:

$ python3 -c 'import sys,csv; csv.Sniffer().sniff(open(sys.argv[1]).read()[:1024])' data/csv_sniff.csv
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/opt/slapgrid/63b26317101f5984dc8eccebab401b64/parts/python3/lib/python3.11/csv.py", line 187, in sniff
    raise Error("Could not determine delimiter")
_csv.Error: Could not determine delimiter