* server-src/driverio.c (update_info_dumper): Do not update if size or
  csize is 0.
* server-src/server_util.c: Do not uses history if size is 0


git-svn-id: https://svn.code.sf.net/p/amanda/code/amanda/trunk@5792 a8d146d6-cc15-0410-8900-af154a0219e0