[gimp] app: fix missing const qualifier.

[Jehan <jehanp src gnome org>]

commit 5ec22b672002af755f2c707f6d21fd8a38096a7a
Author: Jehan <jehan girinstud io>
Date:   Mon Dec 30 00:23:21 2019 +0100

    app: fix missing const qualifier.
    
    Thanks to frogonia for noticing.

 app/core/gimp-utils.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/app/core/gimp-utils.c b/app/core/gimp-utils.c
index 824cfd8307..8fd7842f3c 100644
--- a/app/core/gimp-utils.c
+++ b/app/core/gimp-utils.c
@@ -627,7 +627,7 @@ is_script (const gchar *filename)
   static gchar **exts = NULL;
 
   const gchar   *ext = strrchr (filename, '.');
-  gchar         *pathext;
+  const gchar   *pathext;
   gint           i;
 
   if (exts == NULL)