fix the leak of the error stack (if PR_Cleanup is not called) and to work around a crash on Windows with MinGW. Thanks to Maks Romih <maksr3@gmail.com> for reporting and tracking down the crash. r=nelson. git-svn-id: svn://10.0.0.236/trunk@253829 18797224-902f-48f8-a5cc-f745e15eee43