Regression from ed6b8c9f which slightly changed the logic
and set bHandled to true by default, thus effectively throwing all
key press events except for Enter and Esc away.

Set key press events (minus Enter & Esc) to bHandled = false and let
them fall through to be dealt with in the base class (ComboBox)

Change-Id: Ie1d857725a7de1d0bed1fd59df7eef5390ae5f3d
Reviewed-on: https://gerrit.libreoffice.org/16407Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>
Tested-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>