[gimp] app: fixing the line art GimpBusyBox visibility.

[Jehan <jehanp src gnome org>]

commit 3a317e72aa3d6f4ebfdae7d476224705f894f77b
Author: Jehan <jehan girinstud io>
Date:   Mon Mar 4 16:55:51 2019 +0100

    app: fixing the line art GimpBusyBox visibility.
    
    Commit bc187cc5cc was a bit wrong as it was possible to get some race
    conditions when changing settings quickly in a short time frame.

 app/core/gimplineart.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/app/core/gimplineart.c b/app/core/gimplineart.c
index 528ec9a6c9..9008caabf5 100644
--- a/app/core/gimplineart.c
+++ b/app/core/gimplineart.c
@@ -565,6 +565,7 @@ gimp_line_art_compute (GimpLineArt *line_art)
        * it can't actually be interrupted.  instead gimp_line_art_compute_cb()
        * bails if the async has been canceled, to avoid accessing the line art.
        */
+      g_signal_emit (line_art, gimp_line_art_signals[COMPUTING_END], 0);
       gimp_cancelable_cancel (GIMP_CANCELABLE (line_art->priv->async));
       g_clear_object (&line_art->priv->async);
     }
@@ -605,8 +606,6 @@ static void
 gimp_line_art_compute_cb (GimpAsync   *async,
                           GimpLineArt *line_art)
 {
-  g_signal_emit (line_art, gimp_line_art_signals[COMPUTING_END], 0);
-
   if (gimp_async_is_canceled (async))
     return;
 
@@ -619,6 +618,7 @@ gimp_line_art_compute_cb (GimpAsync   *async,
       line_art->priv->closed  = g_object_ref (result->closed);
       line_art->priv->distmap = result->distmap;
       result->distmap  = NULL;
+      g_signal_emit (line_art, gimp_line_art_signals[COMPUTING_END], 0);
     }
 
   g_clear_object (&line_art->priv->async);