[gimp] app: don't print a NULL insensitive action reason.

[Jehan <jehanp src gnome org>]

commit c8020c20a5af439a317b309767687948b930b7e0
Author: Jehan <jehan girinstud io>
Date:   Sat Apr 24 23:26:33 2021 +0200

    app: don't print a NULL insensitive action reason.
    
    Print an empty string itself, otherwise it actually displays "(null)".
    And anyway it's not clean code to use a NULL pointer in a printf format.

 app/widgets/gimpaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/app/widgets/gimpaction.c b/app/widgets/gimpaction.c
index 982e8f5322..a175e9ded5 100644
--- a/app/widgets/gimpaction.c
+++ b/app/widgets/gimpaction.c
@@ -414,7 +414,7 @@ gimp_action_set_proxy_tooltip (GimpAction *action,
                             "<i><span weight='light'>%s</span></i>", /* Inactive reason */
                             tooltip,
                             escaped_reason && tooltip ? "\n" : "",
-                            escaped_reason);
+                            escaped_reason ? escaped_reason : "");
 
   if (tooltip || escaped_reason)
     gimp_help_set_help_data_with_markup (proxy, markup,