Initialize MetaStoreWriter self._file to None
Initialize MetaStoreWriter self._file to None

Without this, if something goes wrong in the constructor self._file
may not be initialized, which causes close(), invoked via __del__(),
to crash.

Thanks to Fabian Bakkum <fabianbakkum@hotmail.com> for reporting the
problem.

Signed-off-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>

jbaber/bup,tjanez/bup,mhoeher/bup,jbaber/bup,pombredanne/bup,pombredanne/bup,jbaber/bup,ToxicFrog/bup,gevaerts/bup,pombredanne/bup,mhoeher/bup,mhoeher/bup,ToxicFrog/bup,gevaerts/bup,jbaber/bup,ToxicFrog/bup,ToxicFrog/bup,mhoeher/bup,pombredanne/bup,ToxicFrog/bup,gevaerts/bup,tjanez/bup,pombredanne/bup,jbaber/bup,tjanez/bup,jbaber/bup,gevaerts/bup,tjanez/bup,tjanez/bup,mhoeher/bup,mhoeher/bup,pombredanne/bup,gevaerts/bup,tjanez/bup