ENH: Updated film default BC for alpha field

src/regionModels/surfaceFilmModels/kinematicSingleLayer/kinematicSingleLayer.C

@@ -521,7 +521,8 @@ kinematicSingleLayer::kinematicSingleLayer
             IOobject::AUTO_WRITE
         ),
         regionMesh(),
-        dimensionedScalar("zero", dimless, 0.0)
+        dimensionedScalar("zero", dimless, 0.0),
+        zeroGradientFvPatchScalarField::typeName
     ),
     U_
     (