clock: fix refcounting bug in gst_clock_set_master.
clock: fix refcounting bug in gst_clock_set_master.

Make sure clock->clockid is unreffed before clock->master.
gst_clock_id_unschedule (clock->clockid) tries to access clock->master. If
clock->master is unreffed before and it's deallocated, _unschedule could access
free'd memory.

krieger-od/gstreamer,krieger-od/gstreamer,lubosz/gstreamer,surround-io/gstreamer,mparis/gstreamer,lovebug356/gstreamer,shelsonjava/gstreamer,justinjoy/gstreamer,justinjoy/gstreamer,cablelabs/gstreamer,StreamUtils/gstreamer,Distrotech/gstreamer,cablelabs/gstreamer,Distrotech/gstreamer,krieger-od/gstreamer,mparis/gstreamer,ahmedammar/platform_external_gst_gstreamer,krieger-od/gstreamer,lovebug356/gstreamer,cfoch/gstreamer,magcius/gstreamer,centricular/gstreamer,ylatuya/gstreamer,cfoch/gstreamer,drothlis/gstreamer,magcius/gstreamer,Distrotech/gstreamer,jpxiong/gstreamer,mrchapp/gstreamer,cablelabs/gstreamer,magcius/gstreamer,collects/gstreamer,cfoch/gstreamer,drothlis/gstreamer,ahmedammar/platform_external_gst_gstreamer,mparis/gstreamer,mrchapp/gstreamer,justinjoy/gstreamer,jpakkane/gstreamer,cfoch/gstreamer,lovebug356/gstreamer,jpxiong/gstreamer,collects/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,lubosz/gstreamer,shelsonjava/gstreamer,magcius/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,centricular/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,justinjoy/gstreamer,ensonic/gstreamer,jpakkane/gstreamer,mparis/gstreamer,mparis/gstreamer,krichter722/gstreamer,ylatuya/gstreamer,collects/gstreamer,mrchapp/gstreamer,Lachann/gstreamer,surround-io/gstreamer,Lachann/gstreamer,cfoch/gstreamer,collects/gstreamer,Lachann/gstreamer,Lachann/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,mrchapp/gstreamer,drothlis/gstreamer,ylatuya/gstreamer,cablelabs/gstreamer,surround-io/gstreamer,jpxiong/gstreamer,centricular/gstreamer,drothlis/gstreamer,centricular/gstreamer,jpakkane/gstreamer,ylatuya/gstreamer,lubosz/gstreamer,lubosz/gstreamer,justinjoy/gstreamer,centricular/gstreamer,ylatuya/gstreamer,ahmedammar/platform_external_gst_gstreamer,krichter722/gstreamer,surround-io/gstreamer,collects/gstreamer,ensonic/gstreamer,Lachann/gstreamer,cablelabs/gstreamer,lubosz/gstreamer,lovebug356/gstreamer,StreamUtils/gstreamer,Distrotech/gstreamer,krieger-od/gstreamer,ahmedammar/platform_external_gst_gstreamer,ensonic/gstreamer,krichter722/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,magcius/gstreamer,krichter722/gstreamer,Distrotech/gstreamer,drothlis/gstreamer,mrchapp/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,ensonic/gstreamer,ahmedammar/platform_external_gst_gstreamer