h265parse: Unref/replace force_key_unit_event in gst_h265_parse_reset

Apply the commit 36a2aca

https://bugzilla.gnome.org/show_bug.cgi?id=754124
diff --git a/gst/videoparsers/gsth265parse.c b/gst/videoparsers/gsth265parse.c
index 56ace3d..d696e8d 100644
--- a/gst/videoparsers/gsth265parse.c
+++ b/gst/videoparsers/gsth265parse.c
@@ -199,7 +199,7 @@
   h265parse->sent_codec_tag = FALSE;
 
   h265parse->pending_key_unit_ts = GST_CLOCK_TIME_NONE;
-  h265parse->force_key_unit_event = NULL;
+  gst_event_replace (&h265parse->force_key_unit_event, NULL);
 
   h265parse->discont = FALSE;