MNT: Safeguard against being passed a bad value for nthr

splinterpolator.h

@@ -1503,7 +1503,7 @@ void Splinterpolator<T>::deconv_along(unsigned int dim)
     ss *= _dim[i];
   }
 
-  if (_nthr==1) { // If we are to run single-threaded
+  if (_nthr<=1) { // If we are to run single-threaded
     SplineColumn  col(mdim,mstep);          // Column helps us do the job
     for (unsigned int l=0; l<rdim[3]; l++) {
       for (unsigned int k=0; k<rdim[2]; k++) {