[libchamplain] Fix an invalid cast if a view is passed a ChamplainLayer instead of a ChamplainSelectionLayer

[Jiří Techet <jiritechet src gnome org>]

commit d9765e75b009172d86f7d1c96df21fc5f075d03a
Author: Emmanuel Rodriguez <emmanuel rodriguez gmail com>
Date:   Tue May 11 21:59:49 2010 +0200

    Fix an invalid cast if a view is passed a ChamplainLayer instead of a ChamplainSelectionLayer
    
    button_release_cb can't assume that all objects in the layer group are
    selection layers. Normal layers are also allowed.

 champlain/champlain-view.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/champlain/champlain-view.c b/champlain/champlain-view.c
index 2256acb..18ef0e5 100644
--- a/champlain/champlain-view.c
+++ b/champlain/champlain-view.c
@@ -1193,12 +1193,16 @@ button_release_cb (ClutterActor *actor,
 
   for (i = 0; i < clutter_group_get_n_children (CLUTTER_GROUP (priv->user_layers)); i++)
     {
-      ChamplainSelectionLayer *layer = CHAMPLAIN_SELECTION_LAYER (clutter_group_get_nth_child (CLUTTER_GROUP (priv->user_layers), i));
+      ClutterActor *actor = CLUTTER_ACTOR (clutter_group_get_nth_child (CLUTTER_GROUP (priv->user_layers), i));
 
-      if (layer && champlain_selection_layer_count_selected_markers (layer ) > 0)
+      if (actor && CHAMPLAIN_IS_SELECTION_LAYER (actor))
         {
-          champlain_selection_layer_unselect_all (layer);
-          found = TRUE;
+          ChamplainSelectionLayer *layer = CHAMPLAIN_SELECTION_LAYER (actor);
+          if (champlain_selection_layer_count_selected_markers (layer) > 0)
+            {
+              champlain_selection_layer_unselect_all (layer);
+              found = TRUE;
+            }
         }
     }