[gegl] buffer: use g_return_if_fail for src/dst in gegl_buffer_set|get

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 80373f34ba9fb43ff1beb249e999ee5fea8fbdec
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Jul 15 12:26:41 2019 +0200

    buffer: use g_return_if_fail for src/dst in gegl_buffer_set|get
    
    Thus getting good indicative error messages; instead of random segfaults
    if these APIs end up being used wrong.

 gegl/buffer/gegl-buffer-access.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gegl/buffer/gegl-buffer-access.c b/gegl/buffer/gegl-buffer-access.c
index 8f0d42aff..6537de4d8 100644
--- a/gegl/buffer/gegl-buffer-access.c
+++ b/gegl/buffer/gegl-buffer-access.c
@@ -1949,6 +1949,7 @@ gegl_buffer_set (GeglBuffer          *buffer,
                  gint                 rowstride)
 {
   g_return_if_fail (GEGL_IS_BUFFER (buffer));
+  g_return_if_fail (src);
   if (format == NULL)
     format = buffer->soft_format;
 
@@ -2348,6 +2349,7 @@ gegl_buffer_get (GeglBuffer          *buffer,
                  GeglAbyssPolicy      repeat_mode)
 {
   g_return_if_fail (GEGL_IS_BUFFER (buffer));
+  g_return_if_fail (dest_buf);
   gegl_buffer_lock (buffer);
   _gegl_buffer_get_unlocked (buffer, scale, rect, format, dest_buf, rowstride, repeat_mode);
   gegl_buffer_unlock (buffer);