fix: Trade empty children option as leaf node

[zombieJ]

原本  children 为 空数组时，上游可以选择是个 bug。但是似乎 bug as feature 特别多。干脆 children 是空数组也当成 leaf 来处理保持一致性。

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[codecov]

Codecov Report

Merging #231 (23372fe) into master (6db62a5) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #231   +/-   ##
=======================================
  Coverage   99.77%   99.77%           
=======================================
  Files          15       15           
  Lines         451      451           
  Branches      110      110           
=======================================
  Hits          450      450           
  Misses          1        1           

Impacted Files	Coverage Δ
src/OptionList/index.tsx	100.00% <100.00%> (ø)
src/utils/commonUtil.ts	100.00% <100.00%> (ø)

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[lgtm-com]

This pull request fixes 1 alert when merging 23372fe into 6db62a5 - view on LGTM.com

fixed alerts:

• 1 for Unused variable, import, function or class

[zombieJ]

+ [email protected]