add judgments if next doesnot exist

[huanmo222]

Please makes sure the items are checked before submitting your PR, thank you!

• Rebase before creating a PR to keep commit history clear.
• Only One commit
• No eslint errors

[codecov-io]

Codecov Report

Merging #3675 into v2 will decrease coverage by 0.17%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##               v2    #3675      +/-   ##
==========================================
- Coverage   18.52%   18.34%   -0.18%     
==========================================
  Files         226      226              
  Lines        5598     5598              
  Branches      725      725              
==========================================
- Hits         1037     1027      -10     
- Misses       4446     4457      +11     
+ Partials      115      114       -1     

Impacted Files	Coverage Δ
src/components/drawer/index.vue	16.66% <0.00%> (-8.34%)	⬇️
src/components/datetime/util.js	36.84% <0.00%> (-2.64%)	⬇️
src/components/datetime/index.vue	24.17% <0.00%> (-2.20%)	⬇️
src/components/datetime/datetimepicker.js	14.07% <0.00%> (-2.17%)	⬇️
src/components/inline-calendar/util.js	69.41% <0.00%> (ø)

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