Fix crash at shutdown in Imaging example.
Fix crash at shutdown in Imaging example.

We had a global imaging report, that was trying to delete the buffer
after the rest of the system shut down.

OSVR/OSVR-Core,godbyk/OSVR-Core,leemichaelRazer/OSVR-Core,leemichaelRazer/OSVR-Core,d235j/OSVR-Core,OSVR/OSVR-Core,Armada651/OSVR-Core,godbyk/OSVR-Core,Armada651/OSVR-Core,Armada651/OSVR-Core,godbyk/OSVR-Core,leemichaelRazer/OSVR-Core,d235j/OSVR-Core,feilen/OSVR-Core,godbyk/OSVR-Core,leemichaelRazer/OSVR-Core,d235j/OSVR-Core,d235j/OSVR-Core,feilen/OSVR-Core,feilen/OSVR-Core,leemichaelRazer/OSVR-Core,feilen/OSVR-Core,godbyk/OSVR-Core,Armada651/OSVR-Core,Armada651/OSVR-Core,OSVR/OSVR-Core,OSVR/OSVR-Core,feilen/OSVR-Core,OSVR/OSVR-Core,d235j/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core