plugins/queue: Use previous knowledge of data type to avoid typecheck.
plugins/queue: Use previous knowledge of data type to avoid typecheck.

We know whether we have a buffer or an event, use that instead of going
trough the expensive GLib typecheck.

The overall instruction fetch reduction introduced by this commit and the
2 previous commits:
* receiving a buffer (_chain) by 20%
* popping a buffer (_loop) by 14%

Numbers acquired through callgrind passing 100000 buffers through queue.

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