caps: unset the parent refcount of the old features before freeing them in gst_caps_set_features()
caps: unset the parent refcount of the old features before freeing them in gst_caps_set_features()

Otherwise gst_caps_features_free() asserts and the features structure is leaked

justinjoy/gstreamer,justinjoy/gstreamer,justinjoy/gstreamer,justinjoy/gstreamer,justinjoy/gstreamer