object: add gst_clear_object()

This is based on g_clear_object(). Basically, you can use this instead
of using g_object_unref (which needs to be preceded by a NULL-check).

Fixes #275

gst/gstobject.c

@@ -295,6 +295,30 @@ gst_object_ref_sink (gpointer object)
   return g_object_ref_sink (object);
 }
 
+/**
+ * gst_clear_object: (skip)
+ * @object_ptr: a pointer to a #GstObject reference
+ *
+ * Clears a reference to a #GstObject.
+ *
+ * @object_ptr must not be %NULL.
+ *
+ * If the reference is %NULL then this function does nothing.
+ * Otherwise, the reference count of the object is decreased using
+ * gst_object_unref() 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_object
+void
+gst_clear_object (volatile GstObject ** object_ptr)
+{
+  g_clear_pointer (object_ptr, gst_object_unref);
+}
+
 /**
  * gst_object_replace:
  * @oldobj: (inout) (transfer full) (nullable): pointer to a place of

gst/gstobject.h

@@ -254,6 +254,10 @@ gpointer	gst_object_ref			(gpointer object);
 GST_API
 void		gst_object_unref		(gpointer object);
 
+GST_API
+void        gst_clear_object (volatile GstObject **object_ptr);
+#define     gst_clear_object(object_ptr) g_clear_pointer ((object_ptr), gst_object_unref)
+
 GST_API
 gpointer        gst_object_ref_sink		(gpointer object);