x265: Fix a deadlock when failing to create the x265enc.

x265: Fix a deadlock when failing to create the x265enc.

The GST_ELEMENT_ERROR will call the gst_object_get_path_string and
use gst_object_get_parent to get the full object path name, which
needs to lock the object. But we are already in a locked context and
so this will cause a deadlock, the pipeline can not exit normally.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2451>