basesrc: Only force-update the duration for dynamic sources when doing the DURATION query
basesrc: Only force-update the duration for dynamic sources when doing the DURATION query

Doing it after every single create() is not very efficient and not necessary.
Especially on network file systems fstat() is not cached and causes network
traffic, making the source possibly unusable slow.

https://bugzilla.gnome.org/show_bug.cgi?id=652037

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