[dia] Improve layer_find_objects_containing_rectangle()

[Hans Breuer <hans src gnome org>]

commit 4463f4eb55b2a26f2f0a1b52f556f2cf782f06cb
Author: Hans Breuer <hans breuer org>
Date:   Sun May 20 20:09:37 2012 +0200

    Improve layer_find_objects_containing_rectangle()
    
    Use g_return_val_if_fail() if NULL is passed in as layer.

 lib/layer.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/lib/layer.c b/lib/layer.c
index 5747d6d..05ff0bd 100644
--- a/lib/layer.c
+++ b/lib/layer.c
@@ -376,6 +376,8 @@ layer_find_objects_containing_rectangle(Layer *layer, Rectangle *rect)
   GList *selected_list;
   DiaObject *obj;
 
+  g_return_val_if_fail  (layer != NULL, NULL);
+
   selected_list = NULL;
   list = layer->objects;
   while (list != NULL) {