[gegl] buffer: in gegl_buffer_set(), allow NULL src buffer if rect is empty

[Ell <ell src gnome org>]

commit 876885898ddf2d29ac9f1bdad13459d28f6f0ef4
Author: Ell <ell_se yahoo com>
Date:   Tue Oct 22 14:41:09 2019 +0300

    buffer: in gegl_buffer_set(), allow NULL src buffer if rect is empty
    
    In gegl_buffer_set(), don't raise a CRITICAL when src is NULL, if
    the provided rect is empty.

 gegl/buffer/gegl-buffer-access.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/gegl/buffer/gegl-buffer-access.c b/gegl/buffer/gegl-buffer-access.c
index 13e0b38b2..1dc9160a9 100644
--- a/gegl/buffer/gegl-buffer-access.c
+++ b/gegl/buffer/gegl-buffer-access.c
@@ -1949,11 +1949,16 @@ gegl_buffer_set (GeglBuffer          *buffer,
                  gint                 rowstride)
 {
   g_return_if_fail (GEGL_IS_BUFFER (buffer));
-  g_return_if_fail (src);
+
+  if (gegl_rectangle_is_empty (rect ? rect : &buffer->extent))
+    return;
+
+  g_return_if_fail (src != NULL);
+
   if (format == NULL)
     format = buffer->soft_format;
 
-  if (rect && (rect->width == 1))
+  if (rect && rect->width == 1)
     {
       if (rect->height == 1)
         {