gst/mxf/mxfdemux.c: Ignore zero sized essence elements. They're often inserted to...

gst/mxf/mxfdemux.c: Ignore zero sized essence elements. They're often inserted to fulfill the streaming requirements.

Original commit message from CVS:
* gst/mxf/mxfdemux.c:
(gst_mxf_demux_handle_generic_container_essence_element):
Ignore zero sized essence elements. They're often inserted
to fulfill the streaming requirements.