a11y/entry: Fix copy-pasteo re 2ndary icon tooltip

The else case was wrongly resetting the accessible description on the
primary icon, which might not exist and can therefore cause a crash.

https://gitlab.gnome.org/GNOME/gtk/issues/1160

gtk/a11y/gtkentryaccessible.c

@@ -604,7 +604,7 @@ gtk_entry_accessible_notify_gtk (GObject    *obj,
             }
           else
             {
-              atk_object_set_description (priv->icons[GTK_ENTRY_ICON_PRIMARY],
+              atk_object_set_description (priv->icons[GTK_ENTRY_ICON_SECONDARY],
                                       "");
             }
         }