[gimp/gimp-2-10] app: in gimp-parallel, fix async-thread shutdown

[Ell <ell src gnome org>]

commit d20170ed6ca2bb62af6e5a71578f0501a5455471
Author: Ell <ell_se yahoo com>
Date:   Sun Jul 1 13:28:06 2018 -0400

    app: in gimp-parallel, fix async-thread shutdown
    
    ... to prevent a potential deadlock.
    
    (cherry picked from commit ff679c66a10828c0adc107dfb14b65ef334b5ffe)

 app/core/gimp-parallel.cc | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/app/core/gimp-parallel.cc b/app/core/gimp-parallel.cc
index 19c917595d..12fb3765c2 100644
--- a/app/core/gimp-parallel.cc
+++ b/app/core/gimp-parallel.cc
@@ -454,6 +454,7 @@ gimp_parallel_run_async_set_n_threads (gint n_threads)
 
   gimp_parallel_run_async_n_threads = n_threads;
 }
+
 static gpointer
 gimp_parallel_run_async_thread_func (GimpParallelRunAsyncThread *thread)
 {
@@ -463,10 +464,10 @@ gimp_parallel_run_async_thread_func (GimpParallelRunAsyncThread *thread)
     {
       GimpParallelRunAsyncTask *task;
 
-      if (thread->quit)
-        break;
-
-      while ((task = (GimpParallelRunAsyncTask *) g_queue_pop_head (&gimp_parallel_run_async_queue)))
+      while (! thread->quit &&
+             (task =
+                (GimpParallelRunAsyncTask *) g_queue_pop_head (
+                                               &gimp_parallel_run_async_queue)))
         {
           g_object_set_data (G_OBJECT (task->async),
                              "gimp-parallel-run-async-link", NULL);
@@ -478,6 +479,9 @@ gimp_parallel_run_async_thread_func (GimpParallelRunAsyncThread *thread)
           g_mutex_lock (&gimp_parallel_run_async_mutex);
         }
 
+      if (thread->quit)
+        break;
+
       g_cond_wait (&gimp_parallel_run_async_cond,
                    &gimp_parallel_run_async_mutex);
     }