Windows: correct ordering of reparse point tests

Windows: correct ordering of reparse point tests

Test for whether an object is a reparse point before testing
whether the provided buffer is large enough to hold the result
if it is.

FSCTL_GET_REPARSE_POINT
FSCTL_SET_REPARSE_POINT
FSCTL_DELETE_REPARSE_POINT

Change-Id: If6c1b9b6e5853d7759f169943310321d408190e0
Reviewed-on: http://gerrit.openafs.org/5748
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>