fix(Search): fix an error when showNoResults=false and arrow down is pressed

[ysugimoto]

This PR fixes an unexpected error on Search module.

When the Search module built with showNoResults={false} props, the <div class="result"> element won't present in DOM. And if a user types cursor-down (keycode: 40) in search input, then it raises an error:

Search.js:260 Uncaught TypeError: Cannot read property 'querySelector' of null
    at Search.eval [as scrollSelectedItemIntoView] (Search.js:260)
    at Search.eval [as moveSelectionBy] (Search.js:252)
    at Array.eval (Search.js:113)
    at EventSet.dispatchEvent (event-stack.development.js:164)
    at EventPool.dispatchEvent (event-stack.development.js:275)
    at eval (event-stack.development.js:341)
    at Map.forEach (<anonymous>)
    at HTMLDocument.eval (event-stack.development.js:340)

This PR can avoid that error by checking menu element existence.

[welcome]

💖 Thanks for opening this pull request! 💖

Here is a list of things that will help get it across the finish line:

• Run yarn lint locally to catch formatting errors. This will fix some errors automatically, commit and push any changes.
• Run yarn test locally to catch errors. This ensures all components still behave as they should.
• Run yarn start to run the doc site locally and try a few pages, ensuring everything is in good working order.
• Include tests when adding/changing behavior.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[codecov-commenter]

Codecov Report

Merging #3938 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3938      +/-   ##
==========================================
- Coverage   99.84%   99.84%   -0.01%     
==========================================
  Files         184      178       -6     
  Lines        3218     3152      -66     
==========================================
- Hits         3213     3147      -66     
  Misses          5        5              

Impacted Files	Coverage Δ
src/modules/Search/Search.js	99.55% <100.00%> (-0.01%)	⬇️
src/elements/Button/Button.js	95.45% <0.00%> (-0.11%)	⬇️
src/modules/Popup/Popup.js	98.71% <0.00%> (-0.04%)	⬇️
src/modules/Tab/Tab.js	100.00% <0.00%> (ø)
src/views/Card/Card.js	100.00% <0.00%> (ø)
src/elements/Flag/Flag.js	100.00% <0.00%> (ø)
src/elements/Icon/Icon.js	100.00% <0.00%> (ø)
src/elements/List/List.js	100.00% <0.00%> (ø)
src/elements/Step/Step.js	100.00% <0.00%> (ø)
... and 44 more

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[layershifter]

Verified, the issue is fixed 👍

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉