[gimp] Issue #3925 - Gimp from git master segfaults when showing preview of exported JPEG file

[Ell <ell src gnome org>]

commit 65530b6aa73bee1855d6e95ba4753b8cffb9370e
Author: Ell <ell_se yahoo com>
Date:   Thu Sep 12 21:01:37 2019 +0300

    Issue #3925 - Gimp from git master segfaults when showing preview of exported JPEG file
    
    In file-jpeg-save, ref the file object when using a preview idle
    to keep it alive.

 plug-ins/file-jpeg/jpeg-save.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/plug-ins/file-jpeg/jpeg-save.c b/plug-ins/file-jpeg/jpeg-save.c
index 908ef9e6a1..87e967d8cb 100644
--- a/plug-ins/file-jpeg/jpeg-save.c
+++ b/plug-ins/file-jpeg/jpeg-save.c
@@ -223,6 +223,7 @@ background_jpeg_save (PreviewPersistent *pp)
 
       /* we cleanup here (load_image doesn't run in the background) */
       g_file_delete (pp->file, NULL, NULL);
+      g_object_unref (pp->file);
 
       g_free (pp);
       prev_p = NULL;
@@ -671,7 +672,7 @@ save_image (GFile        *file,
       pp->buffer      = buffer;
       pp->format      = format;
       pp->src         = NULL;
-      pp->file        = file;
+      pp->file        = g_object_ref (file);
       pp->abort_me    = FALSE;
 
       g_warn_if_fail (prev_p == NULL);