supply a default to switch for preferred C++ behavior

Vector/ChangeLog

+2014-11-20 Lynn Garren <garren@fnal.gov> 
+
+  * Vector/ThreeVector.icc: inline Hep3Vector::operator () (int i)
+
 ==============================
 18.08.14 Release CLHEP-2.2.0.3
 ==============================

Vector/Vector/ThreeVector.icc

@@ -47,8 +47,9 @@ inline double Hep3Vector::operator () (int i) const {
     return y();
   case Z:
     return z();
+  default:
+    return 0.;
   }
-  return 0.;
 }
 
 inline double & Hep3Vector::operator () (int i) {
@@ -60,8 +61,9 @@ inline double & Hep3Vector::operator () (int i) {
     return dy;
   case Z:
     return dz;
+  default:
+    return dummy;
   }
-  return dummy;
 }
 
 // --------------