Bugfix for interIsoFoam/isoAdvector

Hello OpenCFD

I've had a number of crash reports for isoAdvector, of which one can be seen here:

https://github.com/isoAdvector/isoAdvector/issues/9

Inspection showed that the division by zero error was caused by cells being touched at just a point or an edge by the isoFace resulting in an isoFace normal of zero length. In a new commit at github/isoAdvector I have modified isoCutCell.C so that such cells are no longer treated as surface cells. Please see the required fix here (isoCutCell.C): https://github.com/isoAdvector/isoAdvector/commit/252a182fb30dd38787a835d82a1c3dfb51a990ae

Kind regards, Johan