gst/gstevent.c: Fix gst_mini_object_make_writable() and gst_event_copy() for events...

gst/gstevent.c: Fix gst_mini_object_make_writable() and gst_event_copy() for events with event structures by setting ...

Original commit message from CVS:
Patch by: Alessandro Decina  <alessandro at nnva org>
* gst/gstevent.c: (_gst_event_copy):
Fix gst_mini_object_make_writable() and gst_event_copy() for events
with event structures by setting the parent refcount address of the
copied structure to the address of the refcount member of the newly
copied event rather than the address of the refcount member of the
original event. Fixes #358737.
* tests/check/gst/gstevent.c: (GST_START_TEST):
Unit test for the above.