basetransform: don't pass NULL outcaps to transform_size on shutdown
basetransform: don't pass NULL outcaps to transform_size on shutdown

gst_pad_get_current_caps() on the source pad might yield NULL caps
if we're being shut down and the source pad has already been
deactivated by the other thread that's changing state. Just bail
out in that case, instead of passing NULL caps to the transform_size
function, which it might not expect.

Fixes spurious warnings in audioresample shutdown unit test.

https://bugzilla.gnome.org/show_bug.cgi?id=693996

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