channel: Abort migration in delayed unref
channel: Abort migration in delayed unref

When channel is unref'ed during migration migrate_channel_event_cb
is called causing a crash by coroutine yielding to nonexistent channel.

The delayed_unref happens for the target host channel and will only occur
when the migration process fails.

As comment in spice_channel_coroutine says:
  Co-routine exits now - the SpiceChannel object may no longer exist,
  so don't do anything else now unless you like SEGVs

Related: rhbz#1318574
Acked-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@redhat.com>

fgouget/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk