collectpads: Don't unref NULL GstCollectData
collectpads: Don't unref NULL GstCollectData

If a pad is removed while a collectpads element (say adder) is in a chain
function waiting to be collected, there is a possibility that an unref happens
on a NULL pointer.

https://bugzilla.gnome.org/show_bug.cgi?id=707536

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