Fix NULL-deference kernel panic on attempt of destroying non-existing ramdisk-backed CTL LUN.
Fix NULL-deference kernel panic on attempt of destroying non-existing
ramdisk-backed CTL LUN.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase