Update emit_data to return true if data was delivered.

This is probably not needed, but for the sake of correctnes it doesn't hurt.

mopidy/audio/actor.py

@@ -231,11 +231,14 @@ class Audio(pykka.ThreadingActor):
 
         Note that the uri must be set to ``appsrc://`` for this to work.
 
+        Returns true if data was delivered.
+
         :param buffer_: buffer to pass to appsrc
         :type buffer_: :class:`gst.Buffer`
+        :rtype: boolean
         """
         source = self._playbin.get_property('source')
-        source.emit('push-buffer', buffer_)
+        return source.emit('push-buffer', buffer_) == gst.FLOW_OK
 
     def emit_end_of_stream(self):
         """

mopidy/backends/spotify/session_manager.py

@@ -115,8 +115,10 @@ class SpotifySessionManager(process.BaseThread, PyspotifySessionManager):
         buffer_ = gst.Buffer(bytes(frames))
         buffer_.set_caps(gst.caps_from_string(capabilites))
 
-        self.audio.emit_data(buffer_)
-        return num_frames
+        if self.audio.emit_data(buffer_).get():
+            return num_frames
+        else:
+            return 0
 
     def play_token_lost(self, session):
         """Callback used by pyspotify"""