Handle None reported as 'deflated_size'

Tests on windows spew out a lot of these errors:

2011-06-24 19:17:27,976 - ubuntuone.SyncDaemon.EQ - ERROR - Error encountered while handling: SYS_QUEUE_ADDED in <ubuntuone.syncdaemon.status_listener.StatusListener object at 0x02E93970>
Traceback (most recent call last):
  File "C:\Users\Test\src\ubuntuone-client\ubuntuone\syncdaemon\event_queue.py", line 291, in _dispatch
    method(**kwargs)
  File "C:\Users\Test\src\ubuntuone-client\ubuntuone\syncdaemon\status_listener.py", line 91, in handle_SYS_QUEUE_ADDED
    self.status_frontend.download_started(command)
  File "C:\Users\Test\src\ubuntuone-client\ubuntuone\status\aggregator.py", line 809, in download_started
    self.aggregator.download_started(command)
  File "C:\Users\Test\src\ubuntuone-client\ubuntuone\status\aggregator.py", line 727, in download_started
    self.update_progressbar()
  File "C:\Users\Test\src\ubuntuone-client\ubuntuone\status\aggregator.py", line 712, in update_progressbar
    sum(self.progress.values())) / sum(self.to_do.values())
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

This is because something reports a None value for either 'deflated_size' or 'n_bytes_written'.