fix double-delete of LOB file

git-svn-id: http://h2database.googlecode.com/svn/trunk@4808 e6896862-9d19-0410-bfb3-e9fa5d50e656
Bugfix

git-svn-id: http://h2database.googlecode.com/svn/trunk@4809 e6896862-9d19-0410-bfb3-e9fa5d50e656