Making a request for a deleted attachment with the wrong rid causes NPE

Steps to reproduce:

• attach a file on any document and then delete it ( not actually relevant )
• make a request for it from the recycle bin using a non-existent rid parameter in the query string (ex: /xwiki/bin/downloadrev/Sandbox/TestPage1/yourfile.jpg?rev=1.1&rid=144 )

Expected result:

• receive a 404 or relevant file not found message

Actual result:

• a NullPointerException is displayed