gst: Fix usage of glib_check_version()
gst: Fix usage of glib_check_version()

It returns NULL if the installed GLib version is as least as
new as the required version and some explanatory string otherwise.

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