audio: run downstream playback queue unconditionally

Run the downstream playback queue even if there are no samples
in the mixing engine buffer. The downstream queue may still have
queued samples.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-id: 20200920171729.15861-7-vr_qemu@t-online.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

audio/audio.c

@@ -1186,6 +1186,9 @@ static void audio_run_out (AudioState *s)
                     }
                 }
             }
+            if (hw->pcm_ops->run_buffer_out) {
+                hw->pcm_ops->run_buffer_out(hw);
+            }
             continue;
         }