Windows: RDR_Initialize must cleanup threads on failure

If RDR_Initialize() fails after instantiating the worker thread
pool it must call RDR_ShutdownFinal() to destroy the pool before
exiting.  Otherwise, the threads will spin endlessly as each
DeviceIoControl call to the redirector fails.

Change-Id: I347a509703a44c6b8ca25a084ea10dc0df801eb9
Reviewed-on: http://gerrit.openafs.org/9860
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>