[grilo] Add verifications to the beginning of functions

[Juan A. Suarez Romero <jasuarez src gnome org>]

commit 10398b269480ab67e0712e305d3d06ad3f2774a4
Author: Joaquim Rocha <jrocha igalia com>
Date:   Fri Jun 11 10:36:29 2010 +0200

    Add verifications to the beginning of functions

 src/grl-metadata-source.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/src/grl-metadata-source.c b/src/grl-metadata-source.c
index d98c6eb..fef9085 100644
--- a/src/grl-metadata-source.c
+++ b/src/grl-metadata-source.c
@@ -746,6 +746,7 @@ grl_metadata_source_filter_writable (GrlMetadataSource *source,
   /* TODO: All these filer_* methods could probably reuse most of the code */
 
   g_return_val_if_fail (GRL_IS_METADATA_SOURCE (source), NULL);
+  g_return_val_if_fail (keys != NULL, NULL);
 
   writable_keys = grl_metadata_source_writable_keys (source);
   if (!writable_keys) {
@@ -790,6 +791,9 @@ grl_metadata_source_setup_full_resolution_mode (GrlMetadataSource *source,
                                                 const GList *keys,
                                                 struct SourceKeyMapList *key_mapping)
 {
+  g_return_if_fail (GRL_IS_METADATA_SOURCE (source));
+  g_return_if_fail (key_mapping != NULL);
+
   key_mapping->source_maps = NULL;
   key_mapping->operation_keys = NULL;
 
@@ -1046,6 +1050,9 @@ grl_metadata_source_supported_operations_impl (GrlMetadataSource *source)
 {
   GrlSupportedOps caps = GRL_OP_NONE;
   GrlMetadataSourceClass *metadata_source_class;
+
+  g_return_val_if_fail (GRL_IS_METADATA_SOURCE (source), caps);
+
   metadata_source_class = GRL_METADATA_SOURCE_GET_CLASS (source);
   if (metadata_source_class->resolve)
     caps |= GRL_OP_RESOLVE;