ARROW-2711: [Python] Fix inference from Pandas column with first empty list

[pitrou]

No description provided.

[xhochy]

+1, LGTM

[codecov-io]

Codecov Report

Merging #2309 into master will increase coverage by 2.39%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2309      +/-   ##
==========================================
+ Coverage   84.37%   86.76%   +2.39%     
==========================================
  Files         293      237      -56     
  Lines       44741    42008    -2733     
==========================================
- Hits        37749    36449    -1300     
+ Misses       6961     5559    -1402     
+ Partials       31        0      -31

Impacted Files	Coverage Δ
cpp/src/arrow/python/numpy_to_arrow.cc	89.08% <100%> (+0.02%)	⬆️
python/pyarrow/tests/test_convert_pandas.py	94.92% <100%> (+0.02%)	⬆️
rust/src/builder.rs
go/arrow/array/numericbuilder.gen.go
rust/src/list.rs
go/arrow/array/util.go
go/arrow/array/bufferbuilder.go
go/arrow/datatype_fixedwidth.go
go/arrow/array/bufferbuilder_byte.go
go/arrow/array/bufferbuilder_numeric.gen.go
... and 49 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 355ff08...859ca93. Read the comment docs.

[wesm]

thanks!