[gegl] buffer: avoid trying to allocate for/access 0x0 extent buffers

[Øyvind Kolås <ok src gnome org>]

commit 7260ef9fa8e5dc251ec6f5e239536b9d8cde9945
Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Jun 1 23:44:09 2017 +0200

    buffer: avoid trying to allocate for/access 0x0 extent buffers

 gegl/buffer/gegl-buffer-access.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gegl/buffer/gegl-buffer-access.c b/gegl/buffer/gegl-buffer-access.c
index 8998ba0..8c3473e 100644
--- a/gegl/buffer/gegl-buffer-access.c
+++ b/gegl/buffer/gegl-buffer-access.c
@@ -1505,7 +1505,7 @@ _gegl_buffer_get_unlocked (GeglBuffer          *buffer,
                                    rowstride);
           g_free (sample_buf);
         }
-      else
+      else if (buf_height && buf_width)
         {
           sample_buf = g_malloc (buf_height * buf_width * bpp);