[gimp] app: fix gimp_parallel_run_async() cancelation

[Ell <ell src gnome org>]

commit 3fa4c01bcf7ab207216099640b2c05452200dab2
Author: Ell <ell_se yahoo com>
Date:   Sun May 27 13:53:02 2018 -0400

    app: fix gimp_parallel_run_async() cancelation
    
    In gimp_parallel_run_async(), when aborting a GimpAsync operation
    in reponse to its "cancel" signal, properly clean up internal data
    attached to the object, to avoid use-after-free if the signal is
    emitted again.

 app/core/gimp-parallel.cc | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/app/core/gimp-parallel.cc b/app/core/gimp-parallel.cc
index c029553363..424d20ec73 100644
--- a/app/core/gimp-parallel.cc
+++ b/app/core/gimp-parallel.cc
@@ -489,6 +489,9 @@ gimp_parallel_run_async_cancel (GimpAsync *async)
 
   if (link)
     {
+      g_object_set_data (G_OBJECT (async),
+                         "gimp-parallel-run-async-link", NULL);
+
       g_slice_free (GimpParallelRunAsyncTask, link->data);
 
       g_queue_delete_link (&gimp_parallel_run_async_queue, link);