[mutter] background: Fix build

[Jasper St. Pierre <jstpierre src gnome org>]

commit d4317ba1e4a16bbdb9182afff42d47fd9612cec8
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Wed Sep 3 11:03:17 2014 -0700

    background: Fix build
    
    These warnings weren't properly working on Owen's machine, so they went
    unchecked.

 src/compositor/meta-background-image.c |    4 ++--
 src/compositor/meta-background.c       |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/src/compositor/meta-background-image.c b/src/compositor/meta-background-image.c
index dff3154..1f32f98 100644
--- a/src/compositor/meta-background-image.c
+++ b/src/compositor/meta-background-image.c
@@ -246,8 +246,8 @@ meta_background_image_cache_purge (MetaBackgroundImageCache *cache,
 {
   MetaBackgroundImage *image;
 
-  g_return_val_if_fail (META_IS_BACKGROUND_IMAGE_CACHE (cache), NULL);
-  g_return_val_if_fail (filename != NULL, NULL);
+  g_return_if_fail (META_IS_BACKGROUND_IMAGE_CACHE (cache));
+  g_return_if_fail (filename != NULL);
 
   image = g_hash_table_lookup (cache->images, filename);
   if (image == NULL)
diff --git a/src/compositor/meta-background.c b/src/compositor/meta-background.c
index bc1a0f9..938ef6a 100644
--- a/src/compositor/meta-background.c
+++ b/src/compositor/meta-background.c
@@ -677,9 +677,9 @@ meta_background_get_texture (MetaBackground         *self,
   cairo_rectangle_int_t monitor_area;
   CoglTexture *texture1, *texture2;
 
-  g_return_if_fail (META_IS_BACKGROUND (self));
+  g_return_val_if_fail (META_IS_BACKGROUND (self), NULL);
   priv = self->priv;
-  g_return_if_fail (monitor_index <= 0 && monitor_index < priv->n_monitors);
+  g_return_val_if_fail (monitor_index <= 0 && monitor_index < priv->n_monitors, NULL);
 
   monitor = &priv->monitors[monitor_index];