Don't hang on exit when forcing composer closed
Don't hang on exit when forcing composer closed

Issue introduced with recent move to DraftManager.  When Geary is
closed with an open composer, the window would hide but the app
itself would hang.  This was due to telling the GearyController that
a close was pending when it was not.  Now, when PENDING is returned,
the draft is saved or discarded (based on user input) and the
DraftManager fully closed, ensuring the I/O operation is flushed and
completed.

githubnemo/geary,martinra/geary,jimbonator/geary,emersion/geary,jimbonator/geary,mjog/geary,glebihan/geary,emersion/geary,glebihan/geary,mjog/geary,AtticHacker/geary,aatishnn/geary,AtticHacker/geary,tshikaboom/geary,robol/geary,aatishnn/geary,glebihan/geary,jimbonator/geary,githubnemo/geary,martinra/geary,AtticHacker/geary,tshikaboom/geary,aatishnn/geary,robol/geary,githubnemo/geary,emersion/geary,tshikaboom/geary,robol/geary,martinra/geary,mjog/geary