[gimp] app: notify GimpProjection::buffer when freeing the projection's buffer

[Ell <ell src gnome org>]

commit bcf2b937d9193b20a3a465b1b4802a6faca5492a
Author: Ell <ell_se yahoo com>
Date:   Wed Sep 4 12:59:23 2019 +0300

    app: notify GimpProjection::buffer when freeing the projection's buffer
    
    ... instead of only when subsequently reallocating it, so that
    listeners can respond to the buffer being freed.

 app/core/gimpprojection.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/app/core/gimpprojection.c b/app/core/gimpprojection.c
index 30374374c6..34537551c5 100644
--- a/app/core/gimpprojection.c
+++ b/app/core/gimpprojection.c
@@ -601,6 +601,8 @@ gimp_projection_free_buffer (GimpProjection  *proj)
 
       g_clear_object (&proj->priv->buffer);
       g_clear_object (&proj->priv->validate_handler);
+
+      g_object_notify (G_OBJECT (proj), "buffer");
     }
 }