srm: Fix NPE

Restored requests don't have an origin principal and cause an NPE.

Target: trunk
Request: 2.9
Require-notes: yes
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.dE>
Acked-by: Albert Rossi <arossi@fnal.gov>
Patch: http://rb.dcache.org/r/7006/