gst/: Fix deserialisation from XML. Set parent manually instead of using gst_bin_add(), since gst_bin_add() will unli...

Original commit message from CVS:
* gst/gstbin.c: (gst_bin_restore_thyself):
* gst/gstxml.c: (gst_xml_make_element):
Fix deserialisation from XML. Set parent manually
instead of using gst_bin_add(), since gst_bin_add()
will unlink all pads of the element being added.
Fixes #341667.