STLpoint: declare operator point() for double-precision only

The base-class provides the point for single-precision.

src/surfMesh/surfaceFormats/stl/STLpoint.H

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2013 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -80,11 +80,13 @@ public:
 
     // Member Operators
 
-        //- Conversion to point
+        #ifdef WM_DP
+        //- Conversion to double-precision point
         inline operator point() const
         {
             return point(x(), y(), z());
         }
+        #endif
 };