VolumeDialog: Prevent hiding the ally stream

* There is a rare case that the ally stream is one of the streams
  we add at the expanded panel. In this case while collapsing we
  would remove the ally stream which results in not showing a
  stream at all. (Steps to reproduce: While receiving a call,
  open the volume panel, expand it and collapse it again.)

* Fix that by testing if the stream to hide while collapsing is the
  ally stream and if it is, do not hide it.

Change-Id: Iab4c57ab3ded2c61124594320d5109a52c77f167