we open it. otherwise, if we go to write it out and it has gotten smaller, we will leave garbage at the end of the file. big thanks to Ken Dowling (kdowling@concentric.net) reporting this bug. a=jar git-svn-id: svn://10.0.0.236/trunk@62030 18797224-902f-48f8-a5cc-f745e15eee43