avidemux: Ensure that tags are valid UTF-8 before adding them to the taglist
avidemux: Ensure that tags are valid UTF-8 before adding them to the taglist

https://bugzilla.gnome.org/show_bug.cgi?id=775219

GrokImageCompression/gst-plugins-good,GStreamer/gst-plugins-good,StreamUtils/gst-plugins-good,stfl/gst-plugins-good,StreamUtils/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GrokImageCompression/gst-plugins-good,StreamUtils/gst-plugins-good,GrokImageCompression/gst-plugins-good,hizukiayaka/gst-plugins-good,pexip/gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good,GrokImageCompression/gst-plugins-good,hizukiayaka/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,hizukiayaka/gst-plugins-good,GStreamer/gst-plugins-good,stfl/gst-plugins-good,hizukiayaka/gst-plugins-good,pexip/gst-plugins-good,StreamUtils/gst-plugins-good