[gimp] pdb: fix gimp-file-save PDB procedure implementation.

[Jehan <jehanp src gnome org>]

commit 0f6e43f0b8f229d988d1a2cee986ac74534a9e98
Author: Jehan <jehan girinstud io>
Date:   Wed Oct 21 18:40:18 2020 +0200

    pdb: fix gimp-file-save PDB procedure implementation.
    
    I fixed the wrong file in my previous commit (it's a generated file!).
    This is the right one.

 pdb/groups/file.pdb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/pdb/groups/file.pdb b/pdb/groups/file.pdb
index 14aa690ab6..8b14de43db 100644
--- a/pdb/groups/file.pdb
+++ b/pdb/groups/file.pdb
@@ -253,7 +253,7 @@ HELP
   GimpProcedure       *proc;
   gint                 i;
 
-  file = g_value_get_object (gimp_value_array_index (args, 3));
+  file = g_value_get_object (gimp_value_array_index (args, 4));
 
   file_proc = gimp_plug_in_manager_file_procedure_find (gimp->plug_in_manager,
                                                         GIMP_FILE_PROCEDURE_GROUP_SAVE,