[gimp/gimp-2-10] libgimpconfig: allow writing empty data in gimp_config_writer_data()

[Ell <ell src gnome org>]

commit 26df575278bdbb8efb9751d68ee19fc6c71d6c60
Author: Ell <ell_se yahoo com>
Date:   Thu Jul 5 22:04:07 2018 -0400

    libgimpconfig: allow writing empty data in gimp_config_writer_data()
    
    (cherry picked from commit 3b228afdbe8158dae5de0e45fd6e2df02b3228f8)

 libgimpconfig/gimpconfigwriter.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/libgimpconfig/gimpconfigwriter.c b/libgimpconfig/gimpconfigwriter.c
index 88f739e82a..09ad40cfcb 100644
--- a/libgimpconfig/gimpconfigwriter.c
+++ b/libgimpconfig/gimpconfigwriter.c
@@ -513,8 +513,8 @@ gimp_config_writer_data (GimpConfigWriter *writer,
   gint i;
 
   g_return_if_fail (writer != NULL);
-  g_return_if_fail (length > 0);
-  g_return_if_fail (data != NULL);
+  g_return_if_fail (length >= 0);
+  g_return_if_fail (data != NULL || length == 0);
 
   if (writer->error)
     return;