Minor change to silence NVIDIA compiler warning

SpMat.h

@@ -1261,7 +1261,7 @@ template<class T>
 const Accumulator<T>& Accumulator<T>::ExtractCol(const SpMat<T>& M, unsigned int c)
 {
   if (_sz != M._m) throw ;
-  if (c<0 || c>(M._n-1)) throw ;
+  if (c>(M._n-1)) throw ;
   if (_no) Reset();
   const std::vector<unsigned int>&      ri = M._ri[c];
   const std::vector<T>&                 val = M._val[c];