avutil/frame: Free destination qp_table_buf in frame_copy_props()

Fixes memleak
Fixes: Ticket4899
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 4099e4a7)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/frame.c

@@ -350,6 +350,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
     dst->qscale_table = NULL;
     dst->qstride      = 0;
     dst->qscale_type  = 0;
+    av_buffer_unref(&dst->qp_table_buf);
     if (src->qp_table_buf) {
         dst->qp_table_buf = av_buffer_ref(src->qp_table_buf);
         if (dst->qp_table_buf) {