Tweak to avoid an SQL query for the more common case of looking up a non-shared calendar.
Tweak to avoid an SQL query for the more common case of looking up a non-shared calendar.

git-svn-id: 0c33e958600270102f91bf5868e396345dde476c@7034 e27351fd-9f3e-4f54-a53b-843176b1656c

red-hood/calendarserver,red-hood/calendarserver,red-hood/calendarserver,red-hood/calendarserver,red-hood/calendarserver,red-hood/calendarserver