ENH: checkMesh: near-zero vol cell. Fixes #808.

src/OpenFOAM/meshes/primitiveMesh/primitiveMeshCheck/primitiveMeshTools.C

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2012-2016 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2017 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2017-2018 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -503,7 +503,7 @@ Foam::tmp<Foam::scalarField> Foam::primitiveMeshTools::cellDeterminant
                 }
             }
 
-            if (nInternalFaces == 0)
+            if (nInternalFaces == 0 || avgArea < ROOTVSMALL)
             {
                 cellDeterminant[celli] = 0;
             }