[SelectInput] Only attach click handler to label if a labelId is passed

[johsunds]

• I have followed (at least) the PR section of the contributing guide.

Spent the last couple of hours trying to figure out why my select input was getting focused when I clicked another completely unrelated element. Turns out, there was an element with id="undefined" for some reason, which caused the SelectInput to add this click listener to it since it calls .getElementById(undefined).

A rare error I suppose, but it couldn't hurt to fix it here 😄

[mui-pr-bot]

Bundle size will be reported once CircleCI build #329146 finishes.

Generated by 🚫 dangerJS against ea0f85f

[michaldudak]

Hi @johsunds, sorry for the delayed response. Would you mind creating before/after sandboxes to help test the changes? You can use this sandbox to build a version with your changes included.

Also, a unit test to verify the implemented behavior would be needed.

[johsunds]

Hi @michaldudak, thanks for the response. Here are the before/after sandboxes.

I will add a unit test later, when I have time.

[mui-bot]

Details of bundle changes

Generated by 🚫 dangerJS against 548693e

[eps1lon]

I think you need to update the branch (e.g. by rebasing).

[siriwatknp]

👋 The migration PR has been merged.

Please follow these steps to make sure that the contents are all updated. (Sorry for the inconvenience)

1. pull latest master from upstream to your branch
2. if your PR has changes on the *.md or demo files, you are likely to encounter conflict because all of them have been moved to the new folder.
   2.1 revert the change on those markdown files you did
   2.2 pull latest master from upstream (you should not see conflict)
   2.3 make the changes again at docs/data/material/*
3. run yarn docs:api
   • you might see the changes in docs/pages/material/api/* if your PR touches some of the components
   • it is okay if there is no changes

If you are struggle with the steps above, feel free to tag @siriwatknp