Fix no schema when CSV is only header

[comphead]

Which issue does this PR close?

Closes #3263 .

Rationale for this change

What changes are included in this PR?

Fix no schema when CSV is only header

Are there any user-facing changes?

[andygrove]

LGTM! Thanks @comphead

[codecov-commenter]

Codecov Report

Merging #3272 (2add83d) into master (92110dd) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3272      +/-   ##
==========================================
- Coverage   85.89%   85.89%   -0.01%     
==========================================
  Files         294      294              
  Lines       53373    53400      +27     
==========================================
+ Hits        45845    45868      +23     
- Misses       7528     7532       +4     

Impacted Files	Coverage Δ
datafusion/core/src/datasource/file_format/csv.rs	98.91% <100.00%> (ø)
datafusion/core/tests/sql/create_drop.rs	95.74% <100.00%> (+0.45%)	⬆️
datafusion/expr/src/window_frame.rs	92.43% <0.00%> (-0.85%)	⬇️
datafusion/expr/src/logical_plan/plan.rs	78.21% <0.00%> (-0.52%)	⬇️
...fusion/optimizer/src/pre_cast_lit_in_comparison.rs	85.60% <0.00%> (+2.27%)	⬆️

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[ursabot]

Benchmark runs are scheduled for baseline = 5ee52d0 and contender = 90a0e7c. 90a0e7c is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java