[PATCH] xwayland: fix a crash on output removal

[Olivier Fourdan]

> Hi Adam, Keith,
> 
> I think we'll need this patch in both branches master and 1.18 to fix a
> segfault in Xwayland on output removal (that one is completely my fault).
> 
> Was discussed with Daniel who suggested the fix on irc some time ago (and
> Daniel gave his R-b on irc, thus the R-b in the commit) but somehow forgot
> to track it and it seems it's not been pushed yet.

Sorry, I mean, _I_ forgot to track it...

> 
> Cheers,
> Olivier
>