structure: add gst_clear_structure()

Basically, you can use this instead of using gst_structure_free (which
needs to be preceded by a NULL-check).

Also fixes #275

gst/gststructure.c

@@ -394,6 +394,30 @@ gst_structure_free (GstStructure * structure)
   g_slice_free1 (sizeof (GstStructureImpl), structure);
 }
 
+/**
+ * gst_clear_structure: (skip)
+ * @structure_ptr: a pointer to a #GstStructure reference
+ *
+ * Clears a reference to a #GstStructure.
+ *
+ * @structure_ptr must not be %NULL.
+ *
+ * If the reference is %NULL then this function does nothing.
+ * Otherwise, the structure is free'd using gst_structure_free() and the
+ * pointer is set to %NULL.
+ *
+ * A macro is also included that allows this function to be used without
+ * pointer casts.
+ *
+ * Since: 1.16
+ **/
+#undef gst_clear_structure
+void
+gst_clear_structure (volatile GstStructure ** structure_ptr)
+{
+  g_clear_pointer (structure_ptr, gst_structure_free);
+}
+
 /**
  * gst_structure_get_name:
  * @structure: a #GstStructure

gst/gststructure.h

@@ -133,6 +133,10 @@ gboolean              gst_structure_set_parent_refcount  (GstStructure        *
 GST_API
 void                  gst_structure_free                 (GstStructure        * structure);
 
+GST_API
+void                  gst_clear_structure                (volatile GstStructure **structure_ptr);
+#define               gst_clear_structure(structure_ptr) g_clear_pointer ((structure_ptr), gst_structure_free)
+
 GST_API
 const gchar *         gst_structure_get_name             (const GstStructure  * structure);