XWIKI-11528: Office viewer fails if the page where the file is attached has a special character in the name (whitespace)
* Ensure the path to the temporary file is fully encoded (canonical form) even if the URL used to access the file is partially decoded (which can happen for instance when XWiki is behind Apache's mode_proxy with nocanon option disabled).

(cherry picked from commit e49257257d1c09b688ba3da5fdb0212f6bd240cd)