downloadbuffer: fix uninitialized variable
downloadbuffer: fix uninitialized variable

surround-io/gstreamer,jpxiong/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,Lachann/gstreamer,centricular/gstreamer,surround-io/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,surround-io/gstreamer,Lachann/gstreamer,surround-io/gstreamer,StreamUtils/gstreamer,jpakkane/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,Lachann/gstreamer,mparis/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,jpxiong/gstreamer,centricular/gstreamer,jpakkane/gstreamer,krichter722/gstreamer,krichter722/gstreamer,mparis/gstreamer,mparis/gstreamer,surround-io/gstreamer,mparis/gstreamer,centricular/gstreamer,krichter722/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer