Canonicalize ServerRoot _before_ checking if it is a directory.

Fixes problem where paths without a directory were rejected with
a horrible error on Win32.

PR:
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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81719 13f79535-47bb-0310-9956-ffa450edef68