avidemux: Stop without posting error on flushing
avidemux: Stop without posting error on flushing

This could just be a normal pipeline shutdown.

StreamUtils/gst-plugins-good,hizukiayaka/gst-plugins-good,StreamUtils/gst-plugins-good,GStreamer/gst-plugins-good,stfl/gst-plugins-good,froggatt/gst-plugins-good-m,StreamUtils/gst-plugins-good,stfl/gst-plugins-good,ikonst/gst-plugins-good,Kurento/gst-plugins-good,froggatt/gst-plugins-good-m,stfl/gst-plugins-good,sebras/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,Kurento/gst-plugins-good,rawoul/gst-plugins-good,GrokImageCompression/gst-plugins-good,pexip/gst-plugins-good,hizukiayaka/gst-plugins-good,ikonst/gst-plugins-good,froggatt/gst-plugins-good-m,Kurento/gst-plugins-good,pexip/gst-plugins-good,Kurento/gst-plugins-good,GStreamer/gst-plugins-good,GrokImageCompression/gst-plugins-good,Kurento/gst-plugins-good,hizukiayaka/gst-plugins-good,GStreamer/gst-plugins-good,hizukiayaka/gst-plugins-good,stfl/gst-plugins-good,StreamUtils/gst-plugins-good,GrokImageCompression/gst-plugins-good,pexip/gst-plugins-good,rawoul/gst-plugins-good,froggatt/gst-plugins-good-m,ikonst/gst-plugins-good,ikonst/gst-plugins-good,rawoul/gst-plugins-good,GrokImageCompression/gst-plugins-good,sebras/gst-plugins-good,sebras/gst-plugins-good,rawoul/gst-plugins-good,sebras/gst-plugins-good,pexip/gst-plugins-good