[gimp] libgimp: fix gimp_item_combo_box_changed()

[Michael Natterer <mitch src gnome org>]

commit 02e27bdbc33b2957e30914b1bedaa3aaafc03091
Author: Michael Natterer <mitch gimp org>
Date:   Fri Aug 30 17:58:18 2019 +0200

    libgimp: fix gimp_item_combo_box_changed()
    
    only checking positive IDs for validity had a purpose, put it back.

 libgimp/gimpitemcombobox.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/libgimp/gimpitemcombobox.c b/libgimp/gimpitemcombobox.c
index 6cf6132d0f..d9d4fbd59b 100644
--- a/libgimp/gimpitemcombobox.c
+++ b/libgimp/gimpitemcombobox.c
@@ -576,7 +576,7 @@ gimp_item_combo_box_changed (GimpIntComboBox *combo_box)
 
   if (gimp_int_combo_box_get_active (combo_box, &item_ID))
     {
-      if (! gimp_item_get_by_id (item_ID))
+      if (item_ID > 0 && ! gimp_item_get_by_id (item_ID))
         {
           GtkTreeModel *model;
           GList        *remove = NULL;