For no good or obvious reason, SfxMedium::StorageCommit_Impl() swallows
embed::UseBackupException if there is a pTempFile, which (as the comment
claims) is "always now".  This results in the temp file actually being
copied to the user-visible file and the SaveAs "succeeding", when it
clearly did not.

Also move the exception throwing to the end of ZipOutputStream::finish()
to avoid more memory leaks.

Change-Id: I448cc43291754ef20adfa6b65916282fcc365a11