use NaN/infinity check that is maybe faster

std/haxe/Json.hx

@@ -105,7 +105,7 @@ class Json {
 		case TInt:
 			add(v);
 		case TFloat:
-			add(!Math.isFinite(v) || Math.isNaN(v) ? "null" : v);
+			add(v+1==v ? null : v);
 		case TFunction:
 			add('"<fun>"');
 		case TClass(c):