thermoSingleLayer: revert change to q function made shortly before the release of OpenFOAM-2.3.1

Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1502

src/regionModels/surfaceFilmModels/thermoSingleLayer/thermoSingleLayer.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2014 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2015 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -257,16 +257,9 @@ tmp<fvScalarMatrix> thermoSingleLayer::q(volScalarField& hs) const
 {
     dimensionedScalar Tstd("Tstd", dimTemperature, 298.15);
 
-    volScalarField htcst(htcs_->h());
-    volScalarField htcwt(htcw_->h());
-
-    const volScalarField mask(pos(delta_ - deltaSmall_));
-
-    forAll(mask, i)
-    {
-        htcst[i] *= max(mask[i], ROOTVSMALL);
-        htcwt[i] *= max(mask[i], ROOTVSMALL);
-    }
+    volScalarField boundedAlpha(max(alpha_, ROOTVSMALL));
+    volScalarField htcst(htcs_->h()*boundedAlpha);
+    volScalarField htcwt(htcw_->h()*boundedAlpha);
 
     htcst.correctBoundaryConditions();
     htcwt.correctBoundaryConditions();