processorAgglomerator masterCoarsest fails on small mesh

Summary

On tiny mesh switch on GAMG with processorAgglomerator masterCoarsest. Fails for scotch decomposition, not for hierarchical.

Example case

cavity.tgz

blockMesh
decomposePar
mpirun  -np 5 icoFoam -parallel -debug-switch GAMGAgglomeration=1

What is the current bug behaviour?

What is the expected correct behavior?

Relevant logs and/or images

Courant Number mean: 0 max: 0
smoothSolver:  Solving for Ux, Initial residual = 1, Final residual = 2.06898e-06, No Iterations 7
smoothSolver:  Solving for Uy, Initial residual = 0, Final residual = 0, No Iterations 0
[1] #0  Foam::error::printStack(Foam::Ostream&)[2] #0  Foam::error::printStack(Foam::Ostream&)[3] #0  Foam::error::printStack(Foam::Ostream&)[4] #0  [0] #0  Foam::error::printStack(Foam::Ostream&)Foam::error::printStack(Foam::Ostream&) at ??:?
 at ??:?
[3] #1  Foam::sigSegv::sigHandler(int) at ??:?
 at ??:?
[2] #1  Foam::sigSegv::sigHandler(int)[4] #1  Foam::sigSegv::sigHandler(int)[1] #1  Foam::sigSegv::sigHandler(int) at ??:?
[0] #1  Foam::sigSegv::sigHandler(int) at ??:?
[3] #2  ? at ??:?

Environment information

• OpenFOAM version : 2112

Possible fixes

@Pawan