pulse - only underrun if no more data has been written

pulse - only underrun if no more data has been written

Original patch from David Henningsson <david.henningsson@canonical.com>

If more data has already been written after the underrun, the underrun
will automatically end and therefore we should not report it or
restart the stream.

[ This patch adds a more check of underrun with a new PA function so
  that the underrun handles works more reliably.  As the feature is
  supported only in a recent version of PA, the underrun handling is
  enabled as default now for the new PA, while it's still disabled for
  older PA.  -- tiwai ]

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>