fvDOM with PBiCGStab solver for Ii

Summary

fvDOM matrix not very convergent

Steps to reproduce

take /tutorials/heatTransfer/buoyantPimpleFoam/thermocoupleTestCase

Change in system/fvSolution the solver for the radiation to:

        solver          PBiCGStab;
        preconditioner  DILU;

        tolerance           1e-4;
        relTol              0;
        minIter             10;

It works with minIter set to 1.

@Sergio