Minor additonal error checking

splinterpolator.h

@@ -108,6 +108,11 @@ public:
   //
   unsigned int NDim() const { return(_ndim); }
   unsigned int Order() const { return(_order); }
+  ExtrapolationType Extrapolation(unsigned int dim) const 
+  { 
+    if (dim >= _ndim) throw SplinterpolatorException("Extrapolation: Invalid dimension");
+    return(_et[dim]);
+  } 
   const std::vector<unsigned int>& Size() const { return(_dim); }
   unsigned int Size(unsigned int dim) const { if (dim > 4) return(0); else return(_dim[dim]);}
   T Coef(unsigned int x, unsigned int y=0, unsigned int z=0) const