Fails when EPUBExportDialog::VersionSelectHdl() does not take the
version from the VCL widget.

Change-Id: I8f77643ffbd7766ecec7bc2e148259765ab635b8
Reviewed-on: https://gerrit.libreoffice.org/42600Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>