Don’t render leftpanel stories tree if stories are empty

[danielsneijers]

Issue: Fixes #1588, Warnings about missing selectedKind and selectedStory on initial page render.

What I did

Stopped the LeftPanel from trying to render a Stories hierarchy tree when there are no stories to render.

Code in client init script of @storybook/react gets executed after LeftPanel gets mounted, so tweaking the code in the react client init script as suggested by @edoroshenko did not have any effect. Instead of making the propTypes in the Stories tree optional it seems more logical to not render it at all when there's no content to render.

How to test

• Go through installation guide (https://storybook.js.org/basics/slow-start-guide/)
• Open http://localhost:9001/ (without query string!)
• Open console

[igor-dv]

It worth extracting this to a function for readability

[codecov]

Codecov Report

Merging #1664 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1664      +/-   ##
==========================================
+ Coverage   21.11%   21.15%   +0.03%     
==========================================
  Files         247      247              
  Lines        5580     5579       -1     
  Branches      672      669       -3     
==========================================
+ Hits         1178     1180       +2     
- Misses       3896     3910      +14     
+ Partials      506      489      -17

Impacted Files	Coverage Δ
...b/ui/src/modules/ui/components/left_panel/index.js	100% <100%> (ø)	⬆️
addons/storyshots/src/storybook-channel-mock.js	0% <0%> (ø)	⬆️
lib/ui/src/libs/key_events.js	23.25% <0%> (ø)	⬆️
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
addons/info/src/components/PropTable.js	22.36% <0%> (ø)	⬆️
addons/info/src/components/markdown/code.js	24.13% <0%> (ø)	⬆️
addons/info/src/components/Props.js	37.2% <0%> (ø)	⬆️
lib/codemod/src/transforms/update-addon-info.js	53.65% <0%> (ø)	⬆️
addons/info/src/components/markdown/htags.js	30% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/handle_routing.js	28.04% <0%> (ø)	⬆️
... and 21 more

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[danielsneijers]

By the way, concerning the codebeat issue: is that something I should fix or is it acceptable because it's a React component render function?

[igor-dv]

Usually we look into these issues, but it depends. @ndelangen, what do you think about this case ? I don't see how it can be improved =)

[ndelangen]

Thank you for this PR @danielsneijers !

The tools like codebeat are helpers to stay alert.

I'm not aiming for 100% score in a list of arbitrary code-analytics tools. The point is to make reviews easier and keep us aware of issues we could solve when we touch code.

Great job on this PR!

[danielsneijers]

Happy to help. Just to clarify, is any action needed from me (codebeat and circleci are still pending) or is one of the owners/members responsible for the updating and merging from this point?

[ndelangen]

Nothing else is required to get this merged, your work on this PR is done!

Will merge it!