Don't crash on resume if there is a blkfront instance which failed to initialise before the suspend. This happens in HVM mode for DVD devices which are handled by the emulator, not blkfront.
Don't crash on resume if there is a blkfront instance which failed to
initialise before the suspend. This happens in HVM mode for DVD devices
which are handled by the emulator, not blkfront.

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