Clicking outside the about dialog should close it

[user202729]

Currently it's not, and the behavior seems confusing.

(On an unrelated note it is also slightly confusing that other dialogs e.g. "generate LaTeX code" also needs to click again on that button or press Escape to close it. But I can't really think of a good way against this, because the dialog is the whole screen so there's no "outside". Perhaps make a [←] button somewhere? Compared to TIO's approach of hiding the whole button list and show a [←] button)