caps: add append_structure_unchecked
caps: add append_structure_unchecked

This is useful when we know that caps is !NULL, writable and structure is
!NULL too.

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