GIcon: NULLify the `type' out param in the sync methods too

Both g_[file|bytes]_icon_load() leave the `type' out parameter
untouched, while the async methods g_[file|bytes]_icon_load_finish()
always set it to NULL.

For consistency's sake NULLify it in the sync methods too.

https://bugzilla.gnome.org/show_bug.cgi?id=700725

gio/gfileicon.c

@@ -288,6 +288,9 @@ g_file_icon_load (GLoadableIcon  *icon,
   stream = g_file_read (file_icon->file,
 			cancellable,
 			error);
+
+  if (stream && type)
+    *type = NULL;
   
   return G_INPUT_STREAM (stream);
 }