[Dashboard][Lens] Empty title is not preserved when returning to dashboard from editor

[dej611]

Describe the bug:

If the user sets the Lens panel title to an empty string, navigating to the Lens editor and returning back to Dashboard makes the title rollback to its previous non-empty state.
It can be reproduced both by cloning a Lens panel with a title and removing it, or importing a chart from library and editing the title: clicking on the Edit in Lens action and returning back to the dashboard in edit mode makes the previous title return.

When in view mode the title gets hidden, so it's not a major issue I think.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[ThomThomson]

While this small bug still exists, I am going to close this for now.

Setting the title to a blank string technically does work, but is absolutely not the preferred way of hiding a panel's title. If the user turns off the show panel title switch instead of using a blank string, it will persist when navigating to lens and back.