Some slices are being reached when they have NULL pointers.
There is probably some sort of intermittant threading race condition
causing this.
Simple error condition hacks to fail a bit more gracefully.

Signed-off-by: Wendell Duncan <wendell.duncan@ge.com>
Merge branch 'CITK+QML' of http://github.com/nocnokneo/MITK into CITK+QML