Bug#779916: m-s-d segfaults when you click on a11y tray icon

[Vlad Orlov]

Hi Mike,

> I presume this is a follow-up of #775212 [1]?

Oh, I actually never saw that one. Well, these patches actually never
made it to 1.8 branch upstream. They're in the master branch.

As opposed to that, my PR cleanly applies to 1.8 branch as it modifies
the file that exists there 
(plugins/a11y-keyboard/msd-a11y-preferences-dialog.c).