Crash since 1b597cee "Fix some slight buggyness in closeView()"

[Olivier JG]

There's been a new easy-to-hit crash in KDev caused by the commit as in
the title.

Open two files in a workingset that's open in two areas.
Close one of the files.
Reopen that file.
/Crash

The problem is that the document doesn't update its views() in time,
making the viewsInOtherAreas number wrong. Is closeView() called from
multiple threads?

This is a pretty easy-to-hit crash, so it should probably be reverted if
there isn't a quick-fix to it.

-Olivier JG