Crash in print spooler if save to PDF selected early.

The first issue is that the save to pdf button is enabled
before the first layout completed and at this point we do
not know anything about the document. The second is that
if a layout is in progress and we select save to pdf we
end up starting the documents UI twice and finishing the
second instance carshes the spooler.

bug:17676878

Change-Id: Id0b1f06e4d377347286c2dde09669d431441234b