buffer: Don't copy POOLED and memory metadata unconditionally
buffer: Don't copy POOLED and memory metadata unconditionally

https://bugzilla.gnome.org/show_bug.cgi?id=751712

StreamUtils/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,centricular/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer