basetransform: fix buffer refcounting
basetransform: fix buffer refcounting

When we fail to allocate an output buffer, set the buffer pointer to NULL or
else the calling function will try to unref it.
Remove some old comments

krieger-od/gstreamer,centricular/gstreamer,ensonic/gstreamer,krichter722/gstreamer,krieger-od/gstreamer,jpakkane/gstreamer,cfoch/gstreamer,krichter722/gstreamer,surround-io/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,collects/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,lubosz/gstreamer,jpakkane/gstreamer,justinjoy/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,lubosz/gstreamer,StreamUtils/gstreamer,collects/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,krieger-od/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,cfoch/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,shelsonjava/gstreamer,lubosz/gstreamer,collects/gstreamer,cfoch/gstreamer,krieger-od/gstreamer,mparis/gstreamer,cablelabs/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,surround-io/gstreamer,Lachann/gstreamer,lovebug356/gstreamer,jpakkane/gstreamer,ensonic/gstreamer,cfoch/gstreamer,justinjoy/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,krichter722/gstreamer,lovebug356/gstreamer,lubosz/gstreamer,centricular/gstreamer,krichter722/gstreamer,collects/gstreamer,surround-io/gstreamer,centricular/gstreamer,cablelabs/gstreamer,StreamUtils/gstreamer,cfoch/gstreamer,jpxiong/gstreamer,collects/gstreamer,mparis/gstreamer,lubosz/gstreamer,Lachann/gstreamer,centricular/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,jpxiong/gstreamer,cablelabs/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,jpakkane/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,cablelabs/gstreamer,cablelabs/gstreamer