codecs: h265decoder: Fix per-slice leak

As documented, slice header parsed via gst_h265_parser_parse_slice_hdr()
should be cleared, otherwise it would result in memory leak.

Part-of: <!1274>

subprojects/gst-plugins-bad/gst-libs/gst/codecs/gsth265decoder.c

@@ -650,6 +650,12 @@ gst_h265_decoder_parse_slice (GstH265Decoder * self, GstH265NalUnit * nalu,
     return GST_FLOW_ERROR;
   }
 
+  /* NOTE: gst_h265_parser_parse_slice_hdr() allocates array
+   * GstH265SliceHdr::entry_point_offset_minus1 but we don't use it
+   * in this h265decoder baseclass at the moment
+   */
+  gst_h265_slice_hdr_free (&priv->current_slice.header);
+
   priv->current_slice.nalu = *nalu;
 
   if (priv->current_slice.header.dependent_slice_segment_flag) {