Bogus

  uno::Reference< awt::XControlModel > xControlModel = xControlModel;

introduced with 6c61b20a "fdo#46808, Convert
awt::UnoControlDialogModel to new style."  Correct fix involves adding missing
"const" in declaration of UpdateHandler::insertControlModel, so implicit
Reference up-cast works.

Change-Id: I8f6d679a38d99188eb893366e9b552974b3c1bf2