Modify bug that show header when not use header

[uyeong]

Issue:

What I did

I have modified bug that show header when not use header.

How to test

When I pass header: false of options, header is displayed

So I have modified code like below image.

[codecov]

Codecov Report

Merging #1297 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1297   +/-   ##
=======================================
  Coverage   13.76%   13.76%           
=======================================
  Files         201      201           
  Lines        4620     4620           
  Branches      506      498    -8     
=======================================
  Hits          636      636           
- Misses       3538     3564   +26     
+ Partials      446      420   -26

Impacted Files	Coverage Δ
addons/info/src/components/Story.js	0% <ø> (ø)	⬆️
app/react/src/client/preview/error_display.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/types/Number.js	8.06% <0%> (ø)	⬆️
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/types/Select.js	7.93% <0%> (ø)	⬆️
.../ui/src/modules/ui/components/left_panel/header.js	27.58% <0%> (ø)	⬆️
lib/ui/src/modules/ui/containers/layout.js	12.5% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-build.js	0% <0%> (ø)	⬆️
.../ui/src/modules/ui/components/layout/dimensions.js	15.62% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
... and 20 more

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[ndelangen]

Looks ok to me,

Please do note that we're very likely going to move the the content of the info addon into a panel.

[ndelangen]

Thanks for this PR @uyeong !

[shilman]

Thanks @uyeong. The same problem was addressed in #1306, but that one is a little cleaner, so I merged it instead. Thanks for your contribution!!!