qtmux: Only write 4 byte zero padding to the Video Sample Description in MOV
qtmux: Only write 4 byte zero padding to the Video Sample Description in MOV

For MP4 this is not defined, and it actually breaks things for MSE in
Chrome if we do this. For MOV this is required by some broken software
but the official specification says it's optional:
https://developer.apple.com/library/content/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html

https://bugzilla.gnome.org/show_bug.cgi?id=777540

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