[gnome-builder] buffer: check for valid signal group before clearing

[Christian Hergert <chergert src gnome org>]

commit a698b9af8ab313f12ffec64774cdb4a1ef9152a9
Author: Christian Hergert <chergert redhat com>
Date:   Thu Jan 4 00:02:18 2018 -0800

    buffer: check for valid signal group before clearing

 src/libide/buffers/ide-buffer.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/libide/buffers/ide-buffer.c b/src/libide/buffers/ide-buffer.c
index e75ad66..b1afec5 100644
--- a/src/libide/buffers/ide-buffer.c
+++ b/src/libide/buffers/ide-buffer.c
@@ -1433,7 +1433,8 @@ ide_buffer_dispose (GObject *object)
       g_clear_object (&priv->change_monitor);
     }
 
-  dzl_signal_group_set_target (priv->diagnostics_manager_signals, NULL);
+  if (priv->diagnostics_manager_signals != NULL)
+    dzl_signal_group_set_target (priv->diagnostics_manager_signals, NULL);
 
   g_clear_pointer (&priv->diagnostics_line_cache, g_hash_table_unref);
   g_clear_pointer (&priv->diagnostics, ide_diagnostics_unref);