gstgoocamera: fix assert in libgoo
gstgoocamera: fix assert in libgoo

in some cases, the camera element's _stop() method will be called properly.  In which case, the second time it is called, the OMX camera element will already be back in the loaded state so trying to turn capture off will result in an abort.

mrchapp/gst-goo,mrchapp/gst-goo