baseparse: make seeking in DEFAULT format work if the subclass can convert for us
baseparse: make seeking in DEFAULT format work if the subclass can convert for us

We only deal in TIME format ourselves, but if the subclass can handle
converting other formats into TIME format, we can support that too.

Fixes seeking in DEFAULT (sample) format with flacparse,
and the flacdec unit test.

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