asfdemux: Don't post error on flushing while reading headers
asfdemux: Don't post error on flushing while reading headers

GrokImageCompression/gst-plugins-ugly,StreamUtils/gst-plugins-ugly,Kurento/gst-plugins-ugly,GStreamer/gst-plugins-ugly,StreamUtils/gst-plugins-ugly,GStreamer/gst-plugins-ugly,StreamUtils/gst-plugins-ugly,Kurento/gst-plugins-ugly,GStreamer/gst-plugins-ugly,GrokImageCompression/gst-plugins-ugly,Kurento/gst-plugins-ugly,GrokImageCompression/gst-plugins-ugly