fix(Radio): icon ref may be undefined

[chenjiahan]

#9462

[codecov-commenter]

Codecov Report

Merging #9504 (3d2b7c3) into 2.x (43b725d) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              2.x    #9504   +/-   ##
=======================================
  Coverage   90.53%   90.53%           
=======================================
  Files         184      184           
  Lines        5178     5178           
  Branches      307      307           
=======================================
  Hits         4688     4688           
  Misses        449      449           
  Partials       41       41           

Impacted Files	Coverage Δ
src/mixins/checkbox.js	100.00% <100.00%> (ø)

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