fix: open prop undefined should not break opening

[christianrank]

When you pass open={undefined}, you are not able to open the picker anymore by clicking.

I want to add a check for undefined in two places, so it doesn't break.

In my use-case I want to close the picker programmatically, but the rest should work like before with click. So I set open to false to close and set it immediately back to undefined then.

[codecov-io]

Codecov Report

Merging #383 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #383   +/-   ##
=======================================
  Coverage   88.31%   88.31%           
=======================================
  Files          10       10           
  Lines         702      702           
  Branches      192      192           
=======================================
  Hits          620      620           
  Misses         69       69           
  Partials       13       13

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c622fae...8575b45. Read the comment docs.

[ant-design-bot]

Deploy preview for rc-calendar failed.

Built with commit 8575b45

https://app.netlify.com/sites/rc-calendar/deploys/5bdc78c0e39e7c5d39e00423