[gnome-photos] source: Assert that built-in Sources have been handled elsewhere

[Debarshi Ray <debarshir src gnome org>]

commit cf6e42101f5f3f93b87951ef0d64406d797a5c69
Author: Debarshi Ray <debarshir gnome org>
Date:   Sun Jan 21 20:38:34 2018 +0100

    source: Assert that built-in Sources have been handled elsewhere

 src/photos-source.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/src/photos-source.c b/src/photos-source.c
index 42c2360c..24e0706c 100644
--- a/src/photos-source.c
+++ b/src/photos-source.c
@@ -62,14 +62,18 @@ EGG_DEFINE_COUNTER (instances, "PhotosSource", "Instances", "Number of PhotosSou
 static gchar *
 photos_source_build_filter_resource (PhotosSource *self)
 {
-  gchar *filter;
+  g_autofree gchar *filter = NULL;
+  gchar *ret_val = NULL;
 
-  if (!self->builtin)
+  g_return_val_if_fail (!self->builtin, NULL);
+
+  if (self->object != NULL)
     filter = g_strdup_printf ("(nie:dataSource (?urn) = '%s')", self->id);
   else
-    filter = g_strdup ("(false)");
+    g_return_val_if_reached (NULL);
 
-  return filter;
+  ret_val = g_steal_pointer (&filter);
+  return ret_val;
 }