[gegl] convert-format: make op pass-through when "format" property is NULL

[Ell <ell src gnome org>]

commit 0e8b024f0eb88d2a3975b3d3fdd8cbe0669c3e55
Author: Ell <ell_se yahoo com>
Date:   Sun Nov 25 14:32:57 2018 -0500

    convert-format: make op pass-through when "format" property is NULL
    
    ... in which case the output format equals the input format.

 operations/core/convert-format.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/operations/core/convert-format.c b/operations/core/convert-format.c
index 695128b0e..0a8a92e5a 100644
--- a/operations/core/convert-format.c
+++ b/operations/core/convert-format.c
@@ -58,7 +58,7 @@ operation_process (GeglOperation        *operation,
 
   input  = (GeglBuffer*) gegl_operation_context_get_object (context, "input");
 
-  if (gegl_buffer_get_format (input) == o->format)
+  if (! o->format || gegl_buffer_get_format (input) == o->format)
     {
       gegl_operation_context_set_object (context, "output", G_OBJECT (input));