[gnome-logs] Fix crash while exporting blank journal

[David King <davidk src gnome org>]

commit 8a639f3074100378d5cc344bf124a5fac2632240
Author: H00ly666 <hecai4237 gmail com>
Date:   Tue Mar 27 22:42:37 2018 +0800

    Fix crash while exporting blank journal
    
    gnome-logs crashes when exporting a blank journal.
    
    This patch add a check against NULL pointers.
    
    Closes #794724.

 src/gl-window.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/src/gl-window.c b/src/gl-window.c
index a06f1d4..c604285 100644
--- a/src/gl-window.c
+++ b/src/gl-window.c
@@ -144,8 +144,14 @@ on_export (GSimpleAction *action,
             g_clear_error (&error);
         }
 
-        g_output_stream_write (G_OUTPUT_STREAM (file_ostream), file_content,
-                               strlen (file_content), NULL, &error);
+        /* Check against NULL pointer to avoid a crash when exporting and there
+         * are no log entries. */
+        if (file_content != NULL)
+        {
+            g_output_stream_write (G_OUTPUT_STREAM (file_ostream), file_content,
+                                   strlen (file_content), NULL, &error);
+        }
+
         if (error != NULL)
         {
             have_error = TRUE;