chore: update bench.c to handle NaN elements

Author: Neerajpathak07

lib/node_modules/@stdlib/stats/base/dnanmeanpn/benchmark/c/benchmark.length.c

@@ -102,7 +102,11 @@ static double benchmark1( int iterations, int len ) {
 	int i;
 
 	for ( i = 0; i < len; i++ ) {
-		x[ i ] = ( rand_double() * 20000.0 ) - 10000.0;
+		if ( rand_double() < 0.2 ) {
+			x[ i ] = 0.0 / 0.0; // NaN
+		} else {
+			x[ i ] = ( rand_double()*20000.0 ) - 10000.0;
+		}
 	}
 	v = 0.0;
 	t = tic();
@@ -136,7 +140,11 @@ static double benchmark2( int iterations, int len ) {
 	int i;
 
 	for ( i = 0; i < len; i++ ) {
-		x[ i ] = ( rand_double() * 20000.0 ) - 10000.0;
+		if ( rand_double() < 0.2 ) {
+			x[ i ] = 0.0 / 0.0; // NaN
+		} else {
+			x[ i ] = ( rand_double()*20000.0 ) - 10000.0;
+		}
 	}
 	v = 0.0;
 	t = tic();