As of JDK version 1.5, show() and hide() in Dialog have been deprecated

Change-Id: If96e40ebe2c59f31ca4e2b81c6583eb7f8d5ec81
Reviewed-on: https://gerrit.libreoffice.org/11873
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>