fix: correct ascii, plain and unicode format when there are no columns

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.62%. Comparing base (051f0ac) to head (aafd0f0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #82 +/- ## ========================================== + Coverage 95.60% 95.62% +0.01% ========================================== Files 60 60 Lines 6694 6715 +21 ========================================== + Hits 6400 6421 +21 Misses 294 294 ```

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Bencher

Report	Tue, March 26, 2024 at 16:41:32 UTC
Project	theseus-rs/rsql
Branch	no-column-table-format
Testbed	localhost

Benchmark	Latency	Latency Results nanoseconds (ns)
postgresql	➖ (view plot)	807530000.000
sqlite	➖ (view plot)	491440.000

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