Fix info upgrade codemod failing when optional description string is not supplied

[danielduan]

Issue:

#2132

What I did

Added a check

How to test

Is this testable with jest or storyshots?
yes

Does this need a new example in the kitchen sink apps?
no

Does this need an update to the documentation?
no

If your answer is yes to any of these, please make sure to include it in your PR.

[Hypnosphi]

LGTM

[Hypnosphi]

Please fix the unit test

[codecov]

Codecov Report

Merging #2138 into master will decrease coverage by <.01%.
The diff coverage is 27.27%.

@@            Coverage Diff            @@
##           master   #2138      +/-   ##
=========================================
- Coverage   21.41%   21.4%   -0.01%     
=========================================
  Files         263     263              
  Lines        5796    5812      +16     
  Branches      701     688      -13     
=========================================
+ Hits         1241    1244       +3     
- Misses       4000    4043      +43     
+ Partials      555     525      -30

Impacted Files	Coverage Δ
...es__/update-addon-info/update-addon-info.output.js	0% <0%> (ø)	⬆️
...res__/update-addon-info/update-addon-info.input.js	0% <0%> (ø)	⬆️
lib/codemod/src/transforms/update-addon-info.js	49.01% <50%> (-2.15%)	⬇️
app/vue/src/server/utils.js	0% <0%> (-53.58%)	⬇️
lib/ui/src/modules/ui/routes.js	0% <0%> (ø)	⬆️
...s/left_panel/stories_tree/tree_decorators_utils.js	45.23% <0%> (ø)	⬆️
...react-native/src/manager/components/PreviewHelp.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/PropField.js	10.63% <0%> (ø)	⬆️
.../ui/src/modules/ui/components/layout/dimensions.js	15.62% <0%> (ø)	⬆️
... and 26 more

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