[gegl] buffer: fix race condition in GeglTileBackendSwap

[Ell <ell src gnome org>]

commit c130b8be9dc43458c752f199c2851629de91a18c
Author: Ell <ell_se yahoo com>
Date:   Mon Dec 17 09:50:59 2018 -0500

    buffer: fix race condition in GeglTileBackendSwap
    
    ... when compressing a tile before pushing to the queue in one
    thread, while changing the swap compression algorithm in another
    thread.

 gegl/buffer/gegl-tile-backend-swap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/gegl/buffer/gegl-tile-backend-swap.c b/gegl/buffer/gegl-tile-backend-swap.c
index 98d48aec6..3c8933d09 100644
--- a/gegl/buffer/gegl-tile-backend-swap.c
+++ b/gegl/buffer/gegl-tile-backend-swap.c
@@ -235,7 +235,7 @@ gegl_tile_backend_swap_push_queue (ThreadParams *params,
         {
           queue_stalls++;
 
-          if (params->tile && compression)
+          if (params->tile && params->block->compression)
             {
               gint     bpp = babl_format_get_bytes_per_pixel (params->format);
               gpointer compressed;
@@ -247,7 +247,8 @@ gegl_tile_backend_swap_push_queue (ThreadParams *params,
               max_compressed_size = params->size * COMPRESSION_MAX_RATIO;
               compressed          = g_malloc (max_compressed_size);
 
-              if (gegl_compression_compress (compression, params->format,
+              if (gegl_compression_compress (params->block->compression,
+                                             params->format,
                                              gegl_tile_get_data (params->tile),
                                              params->size / bpp,
                                              compressed, &compressed_size,