snappy has issues with degenerate mesh distributions

To reproduce:

• blockMesh
• manual decomposition with all cells on single processor
• snappy: fails during castellate

partial log:

Feature refinement iteration 0
------------------------------
[4] #0  Foam::error::printStack(Foam::Ostream&)[5] #0  Foam::error::printStack(Foam::Ostream&)[1] #0  Foam::error::printStack(Foam::Ostream&)[2] #0  Foam::error::printStack(Foam::Ostream&)[3] #0  Foam::error::printStack(Foam::Ostream&) at ??:?

@Mattijs @landmann @sma

snappyMultiRegionHeater-debug.tar.bz2