Superres recode: fix memory leak.

Earlier, copy_buffer in CODING_CONTEXT was allocated, but not freed.

Change-Id: Iaaab21d3d8f9187a50466ff7866349465561faf2

av1/encoder/encoder.c

diff --git a/av1/encoder/encoder.c b/av1/encoder/encoder.c
index 989c6e1..6bb1e59 100644
--- a/av1/encoder/encoder.c
+++ b/av1/encoder/encoder.c
@@ -5832,6 +5832,10 @@
   if (!frame_is_intra_only(&cpi->common)) release_scaled_references(cpi);
 }
 
+static void release_copy_buffer(CODING_CONTEXT *cc) {
+  aom_free_frame_buffer(&cc->copy_buffer);
+}
+
 static int encode_with_and_without_superres(AV1_COMP *cpi, size_t *size,
                                             uint8_t *dest,
                                             int *largest_tile_id) {
@@ -5954,6 +5958,8 @@
     *largest_tile_id = largest_tile_id2;
   }
 
+  release_copy_buffer(&cpi->coding_context);
+
   return err;
 }
 #endif  // CONFIG_SUPERRES_IN_RECODE