[Fix] wrong startPos calculation when popup dialog

[filod]

No description provided.

[googlebot]

Thanks for your pull request.

It looks like this may be your first contribution to a Google open source project, in which case you'll need to sign a Contributor License Agreement (CLA) at https://cla.developers.google.com/.

If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check the information on your CLA or see this help article on setting the email on your git commits.

Once you've done that, please reply here to let us know. If you signed the CLA as a corporation, please let us know the company's name.

[Frank3K]

I can confirm this fix works. Nice one.

[ajoslin]

Thank you! needed to be done.

@Flod I want to merge this for the release I'm pushing in a few minutes, but you haven't signed the CLA. I'm going to go ahead and put this fix in on my own and credit you.