Windows: AFSTearDownFcbExtents count extents properly

Windows: AFSTearDownFcbExtents count extents properly

Fcb->Specific.File.ExtentsCount cannot be used directly
in the for loop conditional because each call to AFSFreeExtent()
decrements the value.  Instead, save the original value to
'lFcbExtentCount' and use that in the loop conditional.

Change-Id: I7b2dc0fbd1cbf0eec2f627f8caad8c973c3437c7
Reviewed-on: http://gerrit.openafs.org/8566
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>